[release 1.5] stubtest: Fix __mypy-replace false positives (#15689) (#15751)

Author: AlexWaygood

mypy/stubtest.py

@@ -496,7 +496,11 @@ def verify_typeinfo(
     )
 
     # Check everything already defined on the stub class itself (i.e. not inherited)
-    to_check = set(stub.names)
+    #
+    # Filter out non-identifier names, as these are (hopefully always?) whacky/fictional things
+    # (like __mypy-replace or __mypy-post_init, etc.) that don't exist at runtime,
+    # and exist purely for internal mypy reasons
+    to_check = {name for name in stub.names if name.isidentifier()}
     # Check all public things on the runtime class
     to_check.update(
         m for m in vars(runtime) if not is_probably_private(m) and m not in IGNORABLE_CLASS_DUNDERS