ci: approve dependabot PRs so auto-merge can go through

.github/workflows/checks.yml

@@ -16,3 +16,25 @@ jobs:
       - uses: prefix-dev/setup-pixi@f00437f565399d418b0acc85936d12c1fb668347 # v0.10.1
       - run: pixi run lint
       - run: pixi run build-docs
+
+  dependabot:
+    needs: [checks]
+    runs-on: ubuntu-latest
+    if: github.event_name == 'pull_request' && github.event.pull_request.user.login == 'dependabot[bot]'
+    permissions:
+      contents: write
+      pull-requests: write
+    steps:
+      - name: Fetch dependabot metadata
+        id: metadata
+        uses: dependabot/fetch-metadata@25dd0e34f4fe68f24cc83900b1fe3fe149efef98 # v3.1.0
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+      - name: Approve and enable auto-merge
+        if: steps.metadata.outputs.update-type != 'version-update:semver-major'
+        run: |
+          gh pr review --approve "$PR_URL"
+          gh pr merge --auto --squash "$PR_URL"
+        env:
+          PR_URL: ${{ github.event.pull_request.html_url }}
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}