CI: Drop branch "setup-ci" from configuration

This was used during setup. Now we are set up.

Author: olleolleolle

.github/workflows/ci.yml

@@ -3,7 +3,8 @@ name: CI
 on:
   pull_request:
   push:
-    branches: [main, setup-ci]
+    branches:
+      - main
   schedule:
     - cron: '0 8 * * 1' # At 8:00 on Monday