Looks like ref has to be a valid branch

For mbed-os-ci-scripts the ref was set to 'triage_test' which was a valid branch for that repo, however it looks like somone deleted that branch causing the script to fail. This commit updates the ref to 'master' which should hopefully fix the issue.

Author: adbridge

.github/workflows/main.yml

@@ -21,7 +21,7 @@ jobs:
           repository: ARMmbed/mbed-os-ci-scripts
           token: ${{ secrets.ISSUE_TRIAGING_PERMS }}
           path: scripts
-          ref: mbed-os-ci-scripts
+          ref: master
 
       - name: Run the script
         run: |