ci: fix contributors workflow (again) (docker-mailserver#3304)

Author: georglauterbach

.github/workflows/contributors.yml

@@ -14,6 +14,7 @@ env:
   # Assign commit authorship to official Github Actions bot:
   GIT_USER: github-actions[bot]
   GIT_EMAIL: 41898282+github-actions[bot]@users.noreply.github.com
+  BRANCH_NAME: contributors-update
 
 jobs:
   add-contributors:
@@ -23,6 +24,11 @@ jobs:
       - name: 'Checkout'
         uses: actions/checkout@v3
 
+      - name: 'Checkout New Branch and Push It'
+        run: |
+          git checkout -b ${{ env.BRANCH_NAME }}
+          git push --force https://${GITHUB_ACTOR}:${GITHUB_TOKEN}@github.com/${GITHUB_REPOSITORY}.git HEAD:${{ env.BRANCH_NAME }}
+
       # See https://github.com/marketplace/actions/auto-add-contributors for reference of the action.
       #
       # This action is not well documented, but it does the job for now. We pin the version in order
@@ -31,6 +37,7 @@ jobs:
         uses: BobAnkh/add-contributors@v0.2.2
         with:
           ACCESS_TOKEN: ${{secrets.GITHUB_TOKEN}}
+          BRANCH: ${{ env.BRANCH_NAME }}
           COMMIT_MESSAGE: 'docs: update `CONTRIBUTORS.md`'
           PATH: /CONTRIBUTORS.md
           CONTRIBUTOR: '## Contributors'
@@ -45,7 +52,8 @@ jobs:
         id: create-pr
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
-          branch: contributors-update
+          base: master
+          branch: ${{ env.BRANCH_NAME }}
           title: 'docs: update `CONTRIBUTORS.md`'
           commit-message: 'docs: update `CONTRIBUTORS.md`'
           delete-branch: true
@@ -70,7 +78,7 @@ jobs:
           token: ${{ secrets.GITHUB_TOKEN }}
           # Skipped workflows are still assigned a "success" status:
           status: success
-          # This should be the correct commit SHA on the contributors-update branch:
+          # This should be the correct commit SHA on ${{ env.BRANCH_NAME }}:
           sha: ${{ steps.create-pr.outputs.pull-request-head-sha }}
           # Name of status check to add/update:
           context: lint