Add PR-only filter to CLA bot (#137)

Author: cliffchapmanrbx

.github/workflows/clabot.yml

@@ -8,6 +8,7 @@ on:
 jobs:
   clabot:
     runs-on: ubuntu-latest
+    if: contains(github.event.comment.html_url, '/pull/') || github.event_name != 'issue_comment'
     steps:
     - name: "CLA Signature Bot"
       uses: roblox/[email protected]