chore: add revert label check (#14853)

.github/mergeable.yml

@@ -55,8 +55,8 @@ mergeable:
       - do: label
         and:
           - must_include:
-              regex: 'feature|bug|improvement|document|chore'
-              message: 'Label must include one of the following: `feature`, `bug`, `improvement`, `document`, `chore`'
+              regex: 'feature|bug|improvement|document|chore|revert'
+              message: 'Label must include one of the following: `feature`, `bug`, `improvement`, `document`, `chore`, `revert`'
           - must_include:
               regex: 'ready-to-merge'
               message: 'Please check if there are PRs that already have a `ready-to-merge` label and can be merged, if exists please merge them first.'