lock policy down a bit (#44427)

Author: gewarren

.github/policies/label-prs.yml

@@ -56,6 +56,8 @@ configuration:
           - payloadType: Pull_Request
           - isActivitySender:
               user: azure-sdk
+          - filesMatchPattern:
+              pattern: docs/azure/includes/*
         then:
           - addLabel:
               label: ":octocat: auto-merge"