ci(build): cancel in progress runs on PRs

Author: ewanharris

.github/workflows/build.yml

@@ -3,6 +3,10 @@ on:
   - pull_request
   - push
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: ${{ github.ref != 'refs/heads/master' }}
+
 jobs:
   Lint:
     runs-on: ubuntu-latest