Checks for release branches (#230)

Including manual triggers, too.

Author: rainersigwald

.github/workflows/dotnet.yml

@@ -4,7 +4,10 @@ on:
   push:
     branches: [ main ]
   pull_request:
-    branches: [ main ]
+    branches: 
+    - main
+    - v*
+  workflow_dispatch:  
 
 jobs:
   build: