gh-128923: fix test_pydoc for object subclasses without __module__ (#128951)

Fix pydoc's docclass() for classes inheriting from object without the `__module__` attribute, like `_testcapi.HeapType`.

Lib/pydoc.py

@@ -1435,7 +1435,8 @@ location listed above.
         # List the built-in subclasses, if any:
         subclasses = sorted(
             (str(cls.__name__) for cls in type.__subclasses__(object)
-             if not cls.__name__.startswith("_") and cls.__module__ == "builtins"),
+             if (not cls.__name__.startswith("_") and
+                 getattr(cls, '__module__', '') == "builtins")),
             key=str.lower
         )
         no_of_subclasses = len(subclasses)

Lib/test/test_pydoc/test_pydoc.py

@@ -556,6 +556,14 @@ class PydocDocTest(unittest.TestCase):
          |      ... and 82 other subclasses
         """
         doc = pydoc.TextDoc()
+        try:
+            # Make sure HeapType, which has no __module__ attribute, is one
+            # of the known subclasses of object. (doc.docclass() used to
+            # fail if HeapType was imported before running this test, like
+            # when running tests sequentially.)
+            from _testcapi import HeapType
+        except ImportError:
+            pass
         text = doc.docclass(object)
         snip = (" |  Built-in subclasses:\n"
                 " |      async_generator\n"