fixup! typing: get_parametrized_fixture_keys, Session._fixturemanager

Author: blueyed

src/_pytest/fixtures.py

@@ -203,7 +203,8 @@ def get_parametrized_fixture_keys(
         cs = item.callspec  # type: ignore[attr-defined]
     except AttributeError:
         return
-    assert isinstance(item, Function)
+    if TYPE_CHECKING:
+        assert isinstance(item, Function)
 
     # cs.indices.items() is random order of argnames.  Need to
     # sort this so that different calls to

src/_pytest/python.py

@@ -12,6 +12,7 @@
 from textwrap import dedent
 from typing import Dict
 from typing import List
+from typing import Optional
 from typing import Tuple
 
 import py