remove explicit ref -- I think it is not needed? (might need for cron?)

.github/workflows/automerge.yml

@@ -26,7 +26,6 @@ jobs:
     steps:
       - uses: actions/checkout@v3
         with:
-          ref: ${{ github.head_ref }}
           fetch-depth: 0  # Ensures all history is fetched
 
       - name: Get date of the last commit