chore: adjust workflow

.github/workflows/set-pr-title.yml

@@ -10,13 +10,20 @@ jobs:
     steps:
       - name: Checkout code
         uses: actions/checkout@v2
+        with:
+          # Fetches the entire commit history so that we can access the first commit
+          fetch-depth: 0
 
       - name: Get first commit message
-        run: echo "FIRST_COMMIT_MESSAGE=$(git log --format=%B -n 1 $(git rev-list --max-parents=0 HEAD))" >> $GITHUB_ENV
+        run: |
+          # Get the SHA of the first commit in the PR
+          FIRST_COMMIT_SHA=$(git log --reverse --format="%H" "${{ github.event.pull_request.base.sha }}..HEAD" | head -n 1)
+          # Get the message of the first commit in the PR
+          FIRST_COMMIT_MESSAGE=$(git log -n 1 --format=%B "$FIRST_COMMIT_SHA")
+          echo "FIRST_COMMIT_MESSAGE=$FIRST_COMMIT_MESSAGE" >> $GITHUB_ENV
 
       - name: Update PR title
-        run: |
-          gh pr edit "$PR_NUMBER" --title "$FIRST_COMMIT_MESSAGE"
+        run: gh pr edit "$PR_NUMBER" --title "$FIRST_COMMIT_MESSAGE"
         env:
           FIRST_COMMIT_MESSAGE: ${{ env.FIRST_COMMIT_MESSAGE }}
           GITHUB_TOKEN: ${{ secrets.PIXELASS_PAT_BLIBLA }}