Add GH workflow to automatically merge dependabot PRs

Author: maltsev

.github/workflows/dependabot-automerge.yml

@@ -0,0 +1,50 @@
+name: dependabot-automerge
+
+on:
+  workflow_run:
+    workflows: ["build"]
+    types: [completed]
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  automerge:
+    if: github.event.workflow_run.conclusion == 'success'
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Merge Dependabot PR if eligible
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const prs = context.payload.workflow_run.pull_requests;
+            if (!prs || prs.length === 0) {
+              core.info('No pull requests associated with this workflow_run.');
+              return;
+            }
+
+            const prNumber = prs[0].number;
+            const { owner, repo } = context.repo;
+            const { data: pr } = await github.rest.pulls.get({ owner, repo, pull_number: prNumber });
+
+            const author = pr.user?.login || '';
+            if (author !== 'dependabot[bot]' && author !== 'dependabot') {
+              core.info(`PR #${prNumber} is not from Dependabot (${author}).`);
+              return;
+            }
+
+            if (pr.mergeable_state !== 'clean') {
+              core.info(`PR #${prNumber} is not mergeable yet (state: ${pr.mergeable_state}).`);
+              return;
+            }
+
+            await github.rest.pulls.merge({
+              owner,
+              repo,
+              pull_number: prNumber,
+              merge_method: 'merge'
+            });
+
+            core.info(`Merged Dependabot PR #${prNumber}.`);