add branch triggers

.github/workflows/docker-build-test.yml

@@ -4,8 +4,10 @@ name: Test actions image build
 
 # Controls when the workflow will run
 on:
+  push:
+    branches: [main]
   # Allow running workflow manually from the Actions tab
-  workflow_dispatch:
+  workflow_dispatch: ~
 
 # Leaving in example for releases. Initially we simply push to 'latest'
 # on: