Add windir to the default list of Windows pass_env variables

Fixes #3302

docs/changelog/3302.bugfix.rst

@@ -0,0 +1 @@
+- Add ``windir`` to the default list of Windows ``pass_env`` environment variables. - by :user:`kurtmckee`

src/tox/tox_env/api.py

@@ -231,6 +231,7 @@ def _default_pass_env(self) -> list[str]:  # noqa: PLR6301
                     "USERPROFILE",  # needed for `os.path.expanduser()`
                     "PATHEXT",  # needed for discovering executables
                     "MSYSTEM",  # controls paths printed format
+                    "WINDIR",  # base path to system executables and DLLs
                 ],
             )
         else:  # pragma: win32 no cover

tests/session/cmd/test_show_config.py

@@ -138,6 +138,7 @@ def test_pass_env_config_default(tox_project: ToxProjectCreator, stdout_is_atty:
         + (["TERM"] if stdout_is_atty else [])
         + (["TMP", "USERPROFILE"] if is_win else ["TMPDIR"])
         + ["VIRTUALENV_*", "http_proxy", "https_proxy", "no_proxy"]
+        + (["WINDIR"] if is_win else [])
     )
     assert pass_env == expected