ci: run docker build on all push and PRs

.github/workflows/docker.yaml

@@ -1,9 +1,6 @@
 name: Create and publish a Docker image
 
-# Configures this workflow to run every time a change is pushed to the branch called `release`.
-on:
-  push:
-    branches: ['main']
+on: [ push, pull_request ]
 
 # Defines two custom environment variables for the workflow. These are used for the Container registry domain, and a name for the Docker image that this workflow builds.
 env: