fix(ci): Enable auto-merge on automated flake.lock PRs

Author: mrjones2014

.github/workflows/update-flake.yml

@@ -13,7 +13,10 @@ jobs:
         run: nix flake update
       - name: Create Pull Request
         uses: peter-evans/create-pull-request@v8
+        id: create-pr
         with:
           commit-message: "flake: update dependencies"
           title: "[automation] update flake dependencies"
           branch: "automation/update-flake-dependencies"
+      - name: Enable PR auto-merge on CI success
+        run: GH_TOKEN="${{ secrets.GITHUB_TOKEN }}" gh pr merge --squash --delete-branch --auto ${{ steps.create-pr.outputs.pull-request-number }}