use `if not TYPE_CHECKING` on `pytest.__getattr__` to prevent type checkers from using it

src/pytest/__init__.py

@@ -1,5 +1,7 @@
 # PYTHON_ARGCOMPLETE_OK
 """pytest: unit and functional testing with Python."""
+from typing import TYPE_CHECKING
+
 from _pytest import __version__
 from _pytest import version_tuple
 from _pytest._code import ExceptionInfo
@@ -165,6 +167,7 @@ __all__ = [
     "yield_fixture",
 ]
 
+if not TYPE_CHECKING:
 
     def __getattr__(name: str) -> object:
         if name == "Instance":