CI: Update GHA config [skipcircle]

Author: effigies

.github/workflows/docker.yml

@@ -8,9 +8,14 @@ on:
   pull_request:
     branches: [ "master", "main", "maint/*" ]
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 env:
   REGISTRY: ghcr.io
   IMAGE_NAME: ${{ github.repository }}
+  FORCE_COLOR: true
 
 jobs:
   build-container: