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

Patch by Vajrasky Kok.
diff --git a/Lib/test/test_email/test_inversion.py b/Lib/test/test_email/test_inversion.py
index 6f5c534..f36e33d 100644
--- a/Lib/test/test_email/test_inversion.py
+++ b/Lib/test/test_email/test_inversion.py
@@ -43,3 +43,7 @@
             """),),
 
             }
+
+
+if __name__ == '__main__':
+    unittest.main()