Allow running CI in branches, but don't publish

Author: ychin

.github/workflows/ci.yaml

@@ -2,8 +2,6 @@ name: MacVim Documentation Build
 
 on:
   push:
-    branches:
-      - 'main'
   schedule:
     - cron: "50 3 * * *" # 3:50 am UTC every day. Just a random time intentionally picked to be not during busy hours.
   workflow_dispatch:
@@ -70,6 +68,8 @@ jobs:
   deploy:
     needs: build
 
+    if: ${{ github.ref == 'refs/heads/main' }}
+
     permissions:
       pages: write      # to deploy to Pages
       id-token: write   # to verify the deployment originates from an appropriate source