Build: Only one build should run at a time, but prefer the most recent addition.

Add concurrency settings to the build workflow.

Author: dd32

.github/workflows/build.yml

@@ -4,6 +4,10 @@ on:
     push:
         branches: [trunk]
 
+concurrency:
+    group: ${{ github.workflow }}
+    cancel-in-progress: true
+
 jobs:
     build:
         runs-on: ubuntu-latest