We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
Cannot list package files
## Description of the problem, including code/CLI snippet

[Listing package files](https://docs.gitlab.com/ee/api/packages.html#list-package-files) appears to be unsupported. The API endpoint was introduced in GitLab 11.8.

## Expected Behavior

Listing package files should be possible.

## Actual Behavior

Listing package files is not possible.

## Specifications

  - python-gitlab version: 2.6.0
  - API version you are using (v3/v4): v4
  - Gitlab server version (or gitlab.com): gitlab.com


PR incoming.

--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `gitlab/v4/objects/packages.py`
Content:
```
1 from gitlab.base import RESTManager, RESTObject
2 from gitlab.mixins import DeleteMixin, GetMixin, ListMixin, ObjectDeleteMixin
3 
4 
5 __all__ = [
6     "GroupPackage",
7     "GroupPackageManager",
8     "ProjectPackage",
9     "ProjectPackageManager",
10 ]
11 
12 
13 class GroupPackage(RESTObject):
14     pass
15 
16 
17 class GroupPackageManager(ListMixin, RESTManager):
18     _path = "/groups/%(group_id)s/packages"
19     _obj_cls = GroupPackage
20     _from_parent_attrs = {"group_id": "id"}
21     _list_filters = (
22         "exclude_subgroups",
23         "order_by",
24         "sort",
25         "package_type",
26         "package_name",
27     )
28 
29 
30 class ProjectPackage(ObjectDeleteMixin, RESTObject):
31     pass
32 
33 
34 class ProjectPackageManager(ListMixin, GetMixin, DeleteMixin, RESTManager):
35     _path = "/projects/%(project_id)s/packages"
36     _obj_cls = ProjectPackage
37     _from_parent_attrs = {"project_id": "id"}
38     _list_filters = (
39         "order_by",
40         "sort",
41         "package_type",
42         "package_name",
43     )
44
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/gitlab/v4/objects/packages.py b/gitlab/v4/objects/packages.py
--- a/gitlab/v4/objects/packages.py
+++ b/gitlab/v4/objects/packages.py
@@ -1,12 +1,13 @@
 from gitlab.base import RESTManager, RESTObject
 from gitlab.mixins import DeleteMixin, GetMixin, ListMixin, ObjectDeleteMixin
 
-
 __all__ = [
     "GroupPackage",
     "GroupPackageManager",
     "ProjectPackage",
     "ProjectPackageManager",
+    "ProjectPackageFile",
+    "ProjectPackageFileManager",
 ]
 
 
@@ -28,7 +29,7 @@
 
 
 class ProjectPackage(ObjectDeleteMixin, RESTObject):
-    pass
+    _managers = (("package_files", "ProjectPackageFileManager"),)
 
 
 class ProjectPackageManager(ListMixin, GetMixin, DeleteMixin, RESTManager):
@@ -41,3 +42,13 @@
         "package_type",
         "package_name",
     )
+
+
+class ProjectPackageFile(RESTObject):
+    pass
+
+
+class ProjectPackageFileManager(ListMixin, RESTManager):
+    _path = "/projects/%(project_id)s/packages/%(package_id)s/package_files"
+    _obj_cls = ProjectPackageFile
+    _from_parent_attrs = {"project_id": "project_id", "package_id": "id"}

{"golden_diff": "diff --git a/gitlab/v4/objects/packages.py b/gitlab/v4/objects/packages.py\n--- a/gitlab/v4/objects/packages.py\n+++ b/gitlab/v4/objects/packages.py\n@@ -1,12 +1,13 @@\n from gitlab.base import RESTManager, RESTObject\n from gitlab.mixins import DeleteMixin, GetMixin, ListMixin, ObjectDeleteMixin\n \n-\n __all__ = [\n     \"GroupPackage\",\n     \"GroupPackageManager\",\n     \"ProjectPackage\",\n     \"ProjectPackageManager\",\n+    \"ProjectPackageFile\",\n+    \"ProjectPackageFileManager\",\n ]\n \n \n@@ -28,7 +29,7 @@\n \n \n class ProjectPackage(ObjectDeleteMixin, RESTObject):\n-    pass\n+    _managers = ((\"package_files\", \"ProjectPackageFileManager\"),)\n \n \n class ProjectPackageManager(ListMixin, GetMixin, DeleteMixin, RESTManager):\n@@ -41,3 +42,13 @@\n         \"package_type\",\n         \"package_name\",\n     )\n+\n+\n+class ProjectPackageFile(RESTObject):\n+    pass\n+\n+\n+class ProjectPackageFileManager(ListMixin, RESTManager):\n+    _path = \"/projects/%(project_id)s/packages/%(package_id)s/package_files\"\n+    _obj_cls = ProjectPackageFile\n+    _from_parent_attrs = {\"project_id\": \"project_id\", \"package_id\": \"id\"}\n", "issue": "Cannot list package files\n## Description of the problem, including code/CLI snippet\r\n\r\n[Listing package files](https://docs.gitlab.com/ee/api/packages.html#list-package-files) appears to be unsupported. The API endpoint was introduced in GitLab 11.8.\r\n\r\n## Expected Behavior\r\n\r\nListing package files should be possible.\r\n\r\n## Actual Behavior\r\n\r\nListing package files is not possible.\r\n\r\n## Specifications\r\n\r\n  - python-gitlab version: 2.6.0\r\n  - API version you are using (v3/v4): v4\r\n  - Gitlab server version (or gitlab.com): gitlab.com\r\n\r\n\r\nPR incoming.\n", "before_files": [{"content": "from gitlab.base import RESTManager, RESTObject\nfrom gitlab.mixins import DeleteMixin, GetMixin, ListMixin, ObjectDeleteMixin\n\n\n__all__ = [\n    \"GroupPackage\",\n    \"GroupPackageManager\",\n    \"ProjectPackage\",\n    \"ProjectPackageManager\",\n]\n\n\nclass GroupPackage(RESTObject):\n    pass\n\n\nclass GroupPackageManager(ListMixin, RESTManager):\n    _path = \"/groups/%(group_id)s/packages\"\n    _obj_cls = GroupPackage\n    _from_parent_attrs = {\"group_id\": \"id\"}\n    _list_filters = (\n        \"exclude_subgroups\",\n        \"order_by\",\n        \"sort\",\n        \"package_type\",\n        \"package_name\",\n    )\n\n\nclass ProjectPackage(ObjectDeleteMixin, RESTObject):\n    pass\n\n\nclass ProjectPackageManager(ListMixin, GetMixin, DeleteMixin, RESTManager):\n    _path = \"/projects/%(project_id)s/packages\"\n    _obj_cls = ProjectPackage\n    _from_parent_attrs = {\"project_id\": \"id\"}\n    _list_filters = (\n        \"order_by\",\n        \"sort\",\n        \"package_type\",\n        \"package_name\",\n    )\n", "path": "gitlab/v4/objects/packages.py"}], "after_files": [{"content": "from gitlab.base import RESTManager, RESTObject\nfrom gitlab.mixins import DeleteMixin, GetMixin, ListMixin, ObjectDeleteMixin\n\n__all__ = [\n    \"GroupPackage\",\n    \"GroupPackageManager\",\n    \"ProjectPackage\",\n    \"ProjectPackageManager\",\n    \"ProjectPackageFile\",\n    \"ProjectPackageFileManager\",\n]\n\n\nclass GroupPackage(RESTObject):\n    pass\n\n\nclass GroupPackageManager(ListMixin, RESTManager):\n    _path = \"/groups/%(group_id)s/packages\"\n    _obj_cls = GroupPackage\n    _from_parent_attrs = {\"group_id\": \"id\"}\n    _list_filters = (\n        \"exclude_subgroups\",\n        \"order_by\",\n        \"sort\",\n        \"package_type\",\n        \"package_name\",\n    )\n\n\nclass ProjectPackage(ObjectDeleteMixin, RESTObject):\n    _managers = ((\"package_files\", \"ProjectPackageFileManager\"),)\n\n\nclass ProjectPackageManager(ListMixin, GetMixin, DeleteMixin, RESTManager):\n    _path = \"/projects/%(project_id)s/packages\"\n    _obj_cls = ProjectPackage\n    _from_parent_attrs = {\"project_id\": \"id\"}\n    _list_filters = (\n        \"order_by\",\n        \"sort\",\n        \"package_type\",\n        \"package_name\",\n    )\n\n\nclass ProjectPackageFile(RESTObject):\n    pass\n\n\nclass ProjectPackageFileManager(ListMixin, RESTManager):\n    _path = \"/projects/%(project_id)s/packages/%(package_id)s/package_files\"\n    _obj_cls = ProjectPackageFile\n    _from_parent_attrs = {\"project_id\": \"project_id\", \"package_id\": \"id\"}\n", "path": "gitlab/v4/objects/packages.py"}]}