ci: improve Dependabot automation

.github/dependabot.yml

@@ -1,15 +1,38 @@
 version: 2
 updates:
-- package-ecosystem: pip
-  directory: "/"
-  schedule:
-    interval: daily
-    time: "02:00"
-  open-pull-requests-limit: 10
+  - package-ecosystem: pip
+    directory: "/"
+    schedule:
+      interval: daily
+      time: "02:00"
+    cooldown:
+      default-days: 7
+    open-pull-requests-limit: 10
+    groups:
+      test-dependencies:
+        patterns:
+          - "pytest*"
+          - "mypy"
+          - "ruff"
+          - "hypothesis"
+          - "safety"
+          - "doc8"
+    commit-message:
+      prefix: "chore"
+      include: "scope"
 
-- package-ecosystem: github-actions
-  directory: "/"
-  schedule:
-    interval: daily
-    time: "02:00"
-  open-pull-requests-limit: 10
+  - package-ecosystem: github-actions
+    directory: "/"
+    schedule:
+      interval: daily
+      time: "02:00"
+    cooldown:
+      default-days: 7
+    open-pull-requests-limit: 10
+    groups:
+      github-actions:
+        patterns:
+          - "*"
+    commit-message:
+      prefix: "ci"
+      include: "scope"

.github/workflows/dependabot-auto-merge.yml

@@ -0,0 +1,25 @@
+name: Dependabot auto-merge
+
+on: pull_request
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  auto-merge:
+    runs-on: ubuntu-latest
+    if: github.actor == 'dependabot[bot]'
+    steps:
+      - name: Fetch Dependabot metadata
+        id: metadata
+        uses: dependabot/fetch-metadata@v2
+
+      - name: Auto-merge patch and minor updates
+        if: |
+          steps.metadata.outputs.update-type == 'version-update:semver-patch' ||
+          steps.metadata.outputs.update-type == 'version-update:semver-minor'
+        run: gh pr merge --auto --squash "$PR_URL"
+        env:
+          PR_URL: ${{ github.event.pull_request.html_url }}
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}