seed isort known_third_party pre-commit hook
@basnijholt question on this. When making changes in https://github.com/pandas-dev/pandas/pull/28164, seed_isort_known_third_party wants to make the following changes.

```
diff --git a/setup.cfg b/setup.cfg
index 43dbac15f5..227defcfe8 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -116,7 +116,7 @@ known_dtypes = pandas.core.dtypes
 known_post_core = pandas.tseries,pandas.io,pandas.plotting
 sections = FUTURE,STDLIB,THIRDPARTY,PRE_LIBS,PRE_CORE,DTYPES,FIRSTPARTY,POST_CORE,LOCALFOLDER
 known_first_party = pandas
-known_third_party = _pytest,announce,dateutil,docutils,flake8,git,hypothesis,jinja2,lxml,matplotlib,numpy,numpydoc,pkg_resources,pyarrow,pytest,pytz,requests,scipy,setuptools,sphinx,sqlalchemy,validate_docstrings,yaml
+known_third_party = announce,dateutil,docutils,flake8,git,hypothesis,jinja2,lxml,matplotlib,numpy,numpydoc,pkg_resources,pyarrow,pytest,pytz,requests,scipy,setuptools,sphinx,sqlalchemy,validate_docstrings,yaml
 multi_line_output = 3
 include_trailing_comma = True
 force_grid_wrap = 0
```

Is that expected? It also takes quite a while to run (5ish seconds). Is that expected?