chore(ci): pin GitHub Actions and enable Dependabot automerge

.github/workflows/changelog.yml

@@ -11,7 +11,7 @@ jobs:
     permissions:
       contents: write
     steps:
-      - uses: actions/checkout@v7
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0
         with:
           fetch-depth: 0
 

.github/workflows/ci.yml

@@ -9,7 +9,7 @@ jobs:
   lint:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v7
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0
       - uses: ruby/setup-ruby@9eb537ca036ebaed86729dcb9309076e4c5c3b74
         with:
           bundler-cache: true
@@ -20,7 +20,7 @@ jobs:
         ruby: [3.3, 3.4, 4.0]
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v7
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0
       - uses: ruby/setup-ruby@9eb537ca036ebaed86729dcb9309076e4c5c3b74
         with:
           bundler-cache: true

.github/workflows/dependabot-automerge.yml

@@ -0,0 +1,37 @@
+name: Dependabot Auto-merge
+
+on:
+  pull_request_target:
+    types:
+      - opened
+      - synchronize
+      - reopened
+
+jobs:
+  automerge:
+    if: github.actor == 'dependabot[bot]'
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      pull-requests: write
+    steps:
+      - name: Fetch Dependabot metadata
+        id: metadata
+        uses: dependabot/fetch-metadata@21025c705c08248db411dc16f3619e6b5f9ea21a
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Enable auto-merge for bundler and GitHub Actions patch/minor updates
+        if: |
+          (
+            steps.metadata.outputs.package-ecosystem == 'bundler' ||
+            steps.metadata.outputs.package-ecosystem == 'github_actions'
+          ) &&
+          (
+            startsWith(steps.metadata.outputs.update-type, 'version-update:semver-patch') ||
+            startsWith(steps.metadata.outputs.update-type, 'version-update:semver-minor')
+          )
+        uses: peter-evans/enable-pull-request-automerge@a660677d5469627102a1c1e11409dd063606628d
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          merge-method: squash