ci: Don't build release images for every commit, only tagged

Author: palango

.github/workflows/build-sign-release-images.yaml

@@ -2,9 +2,6 @@ name: Build and Sign Blockchain Release Images
 
 on:
   push:
-    branches:
-      # Matches i.e: release/1.9.x
-      - 'release/[0-9]+.[0-9]+.x'
     tags:        
       - 'v[0-9]+.[0-9]+.[0-9]+(?:-\S+(?:\.\d+)*)*'
   workflow_dispatch: