Add __name__ == "__main__" guards to test scripts

R=tvanderlippe@chromium.org

Change-Id: I80d623cd1eb7c87386e8619e4dd7c568f79c5a67
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/1884555
Auto-Submit: Yang Guo <yangguo@chromium.org>
Reviewed-by: Mike Jackson <mjackson@microsoft.com>
Commit-Queue: Yang Guo <yangguo@chromium.org>
diff --git a/scripts/run_tests.py b/scripts/run_tests.py
index 9755526..36aeed5 100755
--- a/scripts/run_tests.py
+++ b/scripts/run_tests.py
@@ -6,4 +6,5 @@
 
 from test import run_unittests
 
-run_unittests.main()
+if __name__ == '__main__':
+    run_unittests.main()