chore: rebase breaking change detector before running (#9284)

Author: Hectorhammett

.github/workflows/release-checks.yaml

@@ -10,6 +10,7 @@ jobs:
   backwards-compatibility-check:
     name: Breaking Change Detector
     runs-on: ubuntu-latest
+    if: ${{ !contains(github.event.pull_request.body, 'BREAKING_CHANGE_REASON=') }}
     steps:
       - uses: actions/checkout@v7
         with:
@@ -18,24 +19,23 @@ jobs:
         uses: shivammathur/setup-php@v2
         with:
           php-version: "8.1"
-      - name: "Ensure that branch is up to date with main branch"
+      - name: "Rebase PR branch onto main branch"
         if: github.event.pull_request.user.login != 'release-please[bot]'
         run: |
-          if ! git merge-base --is-ancestor origin/main ${{ github.event.pull_request.head.sha }}; then
-            echo "PR branch is out of date with main. Please merge or rebase main into your branch to avoid false BC break detections."
+          git config user.name "Github Actions"
+          git config user.email "actions@github.com"
+          git checkout ${{ github.event.pull_request.head.sha }}
+          if ! git rebase origin/main; then
+            echo "Failed to rebase PR branch onto main. There may be conflicts. Please resolve conflicts or rebase manually."
             exit 1
           fi
       - name: "Install dependencies"
         run: composer global require "roave/backward-compatibility-check:^8.2"
       - name: "Check for BC breaks"
         if: github.event.pull_request.user.login != 'release-please[bot]'
-        # Ensure the build still passes by adding BREAKING_CHANGE_REASON=[reason] to the PR description.
-        continue-on-error: ${{ contains(github.event.pull_request.body, 'BREAKING_CHANGE_REASON=') }}
         run: |
           ~/.composer/vendor/bin/roave-backward-compatibility-check --from=origin/main --format=github-actions
       - name: "Check for BC label"
-        # Ensure the build still passes by adding BREAKING_CHANGE_REASON=[reason] to the PR description.
-        continue-on-error: ${{ contains(github.event.pull_request.body, 'BREAKING_CHANGE_REASON=') }}
         run: |
           if [[ "true" == "${{ contains(github.event.pull_request.title, '!:') }}" ]]; then
             echo "Breaking change label found in PR title"