python: change pytest pkg/__init__.py to only collect the __init__.py Module

Previously it would collect the entire package, but this is not what
users expect.

Refs #3749
Fixes #8976
Fixes #9263
Fixes #9313

testing/test_nose.py

@@ -504,7 +504,7 @@ def test_nose_setup_skipped_if_non_callable(pytester: Pytester) -> None:
             pass
         """,
     )
-    result = pytester.runpytest(p, "-p", "nose")
+    result = pytester.runpytest(p.parent, "-p", "nose")
     assert result.ret == 0