fix(mgb): fix dump_with_testcase.py's crash with --output-strip-info when json file does not exist

GitOrigin-RevId: 8f56c43d1e154c845df2c51fb80c65aca5c83a5d

sdk/load-and-run/dump_with_testcase_mge.py

@@ -475,7 +475,8 @@ def main():
             args.output,
             output_mgbvars,
             append=True,
-            output_strip_info=args.output_strip_info)
+            output_strip_info=args.output_strip_info,
+            append_json=True)
 
 if __name__ == '__main__':
     main()