Add workflow to bump Bundler version automatically

Author: philippthun

.github/workflows/bump_bundler_version.yml

@@ -0,0 +1,61 @@
+name: Bump Bundler Version
+
+on:
+  workflow_dispatch:
+  push:
+    branches: [ develop ]
+    paths:
+      - '.ruby-version'
+
+jobs:
+  bump-bundler:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      pull-requests: write
+    env:
+      BUNDLE_GEMFILE: ${{ github.workspace }}/spec/Gemfile
+    steps:
+      - uses: hmarr/debug-action@v3
+      - uses: actions/checkout@v5
+      - uses: ruby/setup-ruby@v1
+        with:
+          bundler-cache: true
+      - name: Update BUNDLED WITH in Gemfile.lock
+        run: |
+          echo "Remove all bundler versions except the default one"
+          gem uninstall bundler -a -x
+
+          ruby -v
+          bundler -v
+
+          # We are modifying the Gemfile.lock, thus have to set frozen to false.
+          bundle config set frozen false
+
+          BUNDLER_VERSION=$(ruby -rbundler -e 'puts Bundler::VERSION')
+          
+          pushd spec
+            echo "Update bundler version in Gemfile.lock"
+            bundle update --bundler=$BUNDLER_VERSION
+          popd
+
+          # Don't commit changes in vendor/bundle folder.
+          echo "vendor/bundle/" >> .git/info/exclude
+
+          if git diff --quiet; then
+            echo "changes=false" >> $GITHUB_ENV
+          else
+            echo "changes=true" >> $GITHUB_ENV
+          fi
+      - name: Create or Update Pull Request
+        if: env.changes == 'true'
+        uses: peter-evans/create-pull-request@v7
+        with:
+          branch: bump-bundler-version-${{ github.ref_name }}
+          title: "Automated Bump of Bundler Version in Gemfile.lock"
+          body: |
+            This PR updates Gemfile.lock to use the default Bundler version.
+          labels: "needs_review"
+          commit-message: "Bump Bundler Version in Gemfile.lock"
+          committer: "ari-wg-gitbot <app-runtime-interfaces@cloudfoundry.org>"
+          author: "ari-wg-gitbot <app-runtime-interfaces@cloudfoundry.org>"