Cancel builds upon a new push

Signed-off-by: Stephen Finucane <[email protected]>

Author: stephenfin

.github/workflows/publish-image.yaml

@@ -3,6 +3,9 @@ name: Publish container image
 on:
   push:
   pull_request:
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
 jobs:
   push_to_registry:
     name: Push container image to GitHub Container Registry