Replace custom checkout logic with actions/checkout in CI workflow

.gitea/workflows/ci.yaml

@@ -10,13 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        run: |
-          if [ -d /tmp/watch-party ]; then
-            cd /tmp/watch-party && git fetch origin && git reset --hard origin/main
-          else
-            git clone https://gitea.home.arpa/nik/watch-party /tmp/watch-party
-          fi
-          cp -r /tmp/watch-party/. .
+        uses: actions/checkout@v4
 
       - name: Write deploy key
         run: |