We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
get_last_root_page template tag not working
### Describe the Bug
<!-- A clear and concise description of what the bug is. -->
The `get_last_root_page` template tag is not working:
https://github.com/Integreat/integreat-cms/blob/develop/src/cms/templatetags/page_filters.py#L10-L20

This is because in the page QuerySet aggregation, the difference() function is used:
https://github.com/Integreat/integreat-cms/blob/a285cb3c74b2a2c501147076338e2b2a70c89bd6/src/cms/models/regions/region.py#L177

After difference(), it is not possible to use filter(), see https://docs.djangoproject.com/en/2.2/ref/models/querysets/#union

This leads to the last drop-region in the page tree being incorrectly tied to the last page in the list, not necessarily the last root page.

### Steps to Reproduce

1. Go to Page tree
2. Drag & drop page to most bottom line

### Expected Behavior
<!-- A clear and concise description of what you expected to happen. -->
The page should be placed next to the last root page

### Actual Behavior
<!-- A clear and concise description of what actually happened. -->
The page is placed next to the last page in the list

### Additional Information
<!-- Add any other context (e.g. logs, screenshots, etc.) about the problem here. -->



--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `src/cms/templatetags/page_filters.py`
Content:
```
1 """
2 This is a collection of tags and filters for :class:`~cms.models.pages.page.Page` objects.
3 """
4 from django import template
5 
6 register = template.Library()
7 
8 
9 @register.simple_tag
10 def get_last_root_page(pages):
11     """
12     This tag returns the last page on the root level.
13 
14     :param pages: The requested page tree
15     :type pages: ~mptt.querysets.TreeQuerySet [ ~cms.models.pages.page.Page ]
16 
17     :return: The last root page of the given :class:`~django.db.models.query.QuerySet`
18     :rtype: ~cms.models.pages.page.Page
19     """
20     return pages.filter(parent=None).last()
21
```
--- 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/src/cms/templatetags/page_filters.py b/src/cms/templatetags/page_filters.py
--- a/src/cms/templatetags/page_filters.py
+++ b/src/cms/templatetags/page_filters.py
@@ -12,9 +12,9 @@
     This tag returns the last page on the root level.
 
     :param pages: The requested page tree
-    :type pages: ~mptt.querysets.TreeQuerySet [ ~cms.models.pages.page.Page ]
+    :type pages: list [ ~cms.models.pages.page.Page ]
 
-    :return: The last root page of the given :class:`~django.db.models.query.QuerySet`
+    :return: The last root page of the given page list
     :rtype: ~cms.models.pages.page.Page
     """
-    return pages.filter(parent=None).last()
+    return list(filter(lambda p: not p.parent, pages))[-1]

{"golden_diff": "diff --git a/src/cms/templatetags/page_filters.py b/src/cms/templatetags/page_filters.py\n--- a/src/cms/templatetags/page_filters.py\n+++ b/src/cms/templatetags/page_filters.py\n@@ -12,9 +12,9 @@\n     This tag returns the last page on the root level.\n \n     :param pages: The requested page tree\n-    :type pages: ~mptt.querysets.TreeQuerySet [ ~cms.models.pages.page.Page ]\n+    :type pages: list [ ~cms.models.pages.page.Page ]\n \n-    :return: The last root page of the given :class:`~django.db.models.query.QuerySet`\n+    :return: The last root page of the given page list\n     :rtype: ~cms.models.pages.page.Page\n     \"\"\"\n-    return pages.filter(parent=None).last()\n+    return list(filter(lambda p: not p.parent, pages))[-1]\n", "issue": "get_last_root_page template tag not working\n### Describe the Bug\r\n<!-- A clear and concise description of what the bug is. -->\r\nThe `get_last_root_page` template tag is not working:\r\nhttps://github.com/Integreat/integreat-cms/blob/develop/src/cms/templatetags/page_filters.py#L10-L20\r\n\r\nThis is because in the page QuerySet aggregation, the difference() function is used:\r\nhttps://github.com/Integreat/integreat-cms/blob/a285cb3c74b2a2c501147076338e2b2a70c89bd6/src/cms/models/regions/region.py#L177\r\n\r\nAfter difference(), it is not possible to use filter(), see https://docs.djangoproject.com/en/2.2/ref/models/querysets/#union\r\n\r\nThis leads to the last drop-region in the page tree being incorrectly tied to the last page in the list, not necessarily the last root page.\r\n\r\n### Steps to Reproduce\r\n\r\n1. Go to Page tree\r\n2. Drag & drop page to most bottom line\r\n\r\n### Expected Behavior\r\n<!-- A clear and concise description of what you expected to happen. -->\r\nThe page should be placed next to the last root page\r\n\r\n### Actual Behavior\r\n<!-- A clear and concise description of what actually happened. -->\r\nThe page is placed next to the last page in the list\r\n\r\n### Additional Information\r\n<!-- Add any other context (e.g. logs, screenshots, etc.) about the problem here. -->\r\n\r\n\n", "before_files": [{"content": "\"\"\"\nThis is a collection of tags and filters for :class:`~cms.models.pages.page.Page` objects.\n\"\"\"\nfrom django import template\n\nregister = template.Library()\n\n\n@register.simple_tag\ndef get_last_root_page(pages):\n    \"\"\"\n    This tag returns the last page on the root level.\n\n    :param pages: The requested page tree\n    :type pages: ~mptt.querysets.TreeQuerySet [ ~cms.models.pages.page.Page ]\n\n    :return: The last root page of the given :class:`~django.db.models.query.QuerySet`\n    :rtype: ~cms.models.pages.page.Page\n    \"\"\"\n    return pages.filter(parent=None).last()\n", "path": "src/cms/templatetags/page_filters.py"}], "after_files": [{"content": "\"\"\"\nThis is a collection of tags and filters for :class:`~cms.models.pages.page.Page` objects.\n\"\"\"\nfrom django import template\n\nregister = template.Library()\n\n\n@register.simple_tag\ndef get_last_root_page(pages):\n    \"\"\"\n    This tag returns the last page on the root level.\n\n    :param pages: The requested page tree\n    :type pages: list [ ~cms.models.pages.page.Page ]\n\n    :return: The last root page of the given page list\n    :rtype: ~cms.models.pages.page.Page\n    \"\"\"\n    return list(filter(lambda p: not p.parent, pages))[-1]\n", "path": "src/cms/templatetags/page_filters.py"}]}