Add checkout step to staging migrations workflow

.github/workflows/staging-migrations.yaml

@@ -15,6 +15,7 @@ jobs:
         id: check_changes
         run: |
           git fetch origin main
+          git checkout ${{ github.ref_name }}
 
           if git diff --name-only origin/main...HEAD | grep -q '^migrations/'; then
             echo "changes=true" >> $GITHUB_ENV