docker ci: run for all pushed branches

Sometimes fixes are also needed for build and testing before going into
main...

Author: manio

.github/workflows/docker-image.yml

@@ -2,7 +2,7 @@ name: Docker Image CI
 
 on:
   push:
-    branches: [ "main" ]
+    branches: [ "*" ]
   pull_request:
     branches: [ "main" ]