chore: fix test_lazy_imports.py to properly trigger module re-initialization

Author: hebaalazzeh

packages/google-auth/tests/transport/test_lazy_imports.py

@@ -25,6 +25,7 @@
 
 def clean_sys_modules():
     """Helper to ensure we start with a clean slate for import testing."""
+    sys.modules.pop("google.auth.transport", None)
     for mod in LAZY_MODULES:
         sys.modules.pop(mod, None)