Closes #18475: add unittest.main() to test_email/test_inversions.

Patch by Vajrasky Kok.

Lib/test/test_email/test_inversion.py

@@ -43,3 +43,7 @@ class TestInversion(TestEmailBase, unittest.TestCase):
             """),),
 
             }
+
+
+if __name__ == '__main__':
+    unittest.main()