Mark OpenApi PRs with area-web-frameworks (#41787)

Author: mkArtakMSFT

.github/fabricbot.json

@@ -1533,6 +1533,7 @@
             "src/Mvc/Mvc.Testing.Tasks/src/",
             "src/Mvc/Mvc.Testing/",
             "src/Mvc/Mvc/",
+            "src/OpenApi/",
             "src/Mvc/perf/"
           ]
         }