Unity Build only on default branch

Otherwise it's unable to get the credentials it needs

Author: sunnamed434

.github/workflows/BitMono.Build.yaml

@@ -87,7 +87,7 @@ jobs:
 
   UnityPackage:
     runs-on: ubuntu-latest
-    if: github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name == github.repository
+    if: (github.event_name == 'push' && github.ref == 'refs/heads/main') || (github.event_name == 'create' && github.event.ref_type == 'tag')
     strategy:
       matrix:
         # Note: