test_threaded_import: Fix unittest.main spelling (GH-93114)

(cherry picked from commit 19710145b496b5e5341630d80be9c400aa792bd1)

Co-authored-by: Florian Bruhin <me@the-compiler.org>
diff --git a/Lib/test/test_importlib/test_threaded_import.py b/Lib/test/test_importlib/test_threaded_import.py
index 76b028e..d37eb29 100644
--- a/Lib/test/test_importlib/test_threaded_import.py
+++ b/Lib/test/test_importlib/test_threaded_import.py
@@ -270,4 +270,4 @@
 
 
 if __name__ == "__main__":
-    unittets.main()
+    unittest.main()