workflows: Add deploy stage to CI pipeline

.github/workflows/ci.yml

@@ -1,9 +1,9 @@
-name: "Test"
+name: "CI"
 on:
-  pull_request:
   push:
+    branches: [main]
 jobs:
-  tests:
+  check:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v5
@@ -13,3 +13,11 @@ jobs:
           name: sebastian-stork
           authToken: "${{ secrets.CACHIX_AUTH_TOKEN }}"
       - run: nix flake --extra-experimental-features pipe-operators check
+  deploy:
+    needs: check
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    steps:
+      - uses: actions/checkout@v5
+      - run: git push origin HEAD:deploy --force