Fix fallback base class when tests run without threading
diff --git a/Lib/packaging/tests/test_command_upload_docs.py b/Lib/packaging/tests/test_command_upload_docs.py
index 4070279..c00f5c1 100644
--- a/Lib/packaging/tests/test_command_upload_docs.py
+++ b/Lib/packaging/tests/test_command_upload_docs.py
@@ -19,7 +19,7 @@
     from packaging.tests.pypi_server import PyPIServerTestCase
 except ImportError:
     threading = None
-    PyPIServerTestCase = object
+    PyPIServerTestCase = unittest.TestCase
 
 
 PYPIRC = """\