.github: implement automatic recreate dependabot workflow

.github/workflows/rebase-dependabot.yml

@@ -0,0 +1,64 @@
+name: rebase-dependabot
+on:
+  push:
+    branches: [ main ]
+
+jobs:
+  dependabot_rebase:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Recreate open dependabot pull-requests
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const { repo: { owner, repo } } = context;
+            const pull_requests = await github.rest.pulls.list({
+                owner,
+                repo,
+                state: 'open',
+                sort: 'long-running',
+                direction: 'asc',
+            })
+
+            for (const { number: pull_number, user } of pull_requests.data) {
+                if (user.login !== 'dependabot[bot]') {
+                    continue;
+                }
+
+                console.log(`Inspecting pull request #${pull_number}`);
+
+                const pull_request = await github.rest.pulls.get({
+                    owner,
+                    repo,
+                    pull_number,
+                });
+                
+                console.log(pull_request);
+
+                // Skip dependabot pull requests which are being worked on
+                if (pull_request.data.commits !== 1) {
+                    console.log('Skipping pull request as it is being worked on');
+                    continue;
+                }
+
+                if (pull_request.data.mergeable === true) {
+                    console.log('Skipping mergeable pull request');
+                    continue;
+                }
+
+                if (pull_request.data.mergeable === null) {
+                    console.log('Skipping pull request with unknown mergeable state');
+                    continue;
+                }
+
+                // Comment to re-create the PR and set no-test
+                github.rest.issues.addLabels({
+                    issue_number: pull_number,
+                    owner,
+                    repo,
+                    labels: ['no-test']
+                });
+
+                // Only process one dependabot at a time.
+                break;
+            }