Only sync back versions on Dependabot update PRs

.github/workflows/rebuild.yml

@@ -11,6 +11,10 @@ jobs:
     runs-on: ubuntu-latest
     if: github.event.label.name == 'Rebuild' || github.event_name == 'workflow_dispatch'
 
+    env:
+      HEAD_REF: ${{ github.event.pull_request.head.ref || github.event.ref }}
+      BASE_BRANCH: ${{ github.event.pull_request.base.ref || 'main' }}
+
     permissions:
       contents: write # needed to push rebuilt commit
       pull-requests: write # needed to comment on the PR
@@ -19,7 +23,7 @@ jobs:
         uses: actions/checkout@v5
         with:
           fetch-depth: 0
-          ref: ${{ github.event.pull_request.head.ref || github.event.ref }}
+          ref: ${{ env.HEAD_REF }}
 
       - name: Remove label
         if: github.event_name == 'pull_request'
@@ -37,8 +41,6 @@ jobs:
 
       - name: Merge in changes from base branch
         id: merge
-        env:
-          BASE_BRANCH: ${{ github.event.pull_request.base.ref || 'main' }}
         run: |
           git fetch origin "$BASE_BRANCH"
 
@@ -73,6 +75,8 @@ jobs:
           python-version: 3.11
 
       - name: Sync back version updates to generated workflows
+        # Only sync back versions on Dependabot update PRs
+        if: startsWith(env.HEAD_REF, 'dependabot/')
         working-directory: pr-checks
         run: |
           python3 sync_back.py -v