CI: Auto-merge Sourcery AI bot PRs

Add a GitHub Actions workflow to automatically merge pull requests from the Sourcery AI bot.

New Features:
- Introduce automated merging of Sourcery AI bot PRs using GitHub Actions.

CI:
- Set up a workflow to automatically merge pull requests opened by the `sourcery-ai[bot]` user. The workflow uses the `gh` CLI to merge the PR with the squash strategy, auto-merge, and delete the branch after merging.

Resolves #6

Author: sourcery-ai[bot]

.github/workflows/merge-sourcery-ai-bot-pr.yml

@@ -0,0 +1,24 @@
+name: Auto-merge Sourcery AI Bot PRs
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+
+permissions:
+  contents: write
+
+env:
+  GH_TOKEN: ${{ secrets.USER_TOKEN }}
+
+jobs:
+  merge-sourcery-pr:
+    runs-on: ubuntu-latest
+    if: github.event.pull_request.user.login == 'sourcery-ai[bot]'
+    steps:
+      - name: Merge Pull Request
+        run: |
+          gh pr merge "${{ github.event.pull_request.number }}" \
+            --squash \
+            --auto \
+            --delete-branch \
+            --repo "${{ github.repository }}"