Add github action concurrency control (#292)

Author: trask

.github/workflows/build-pull-request.yml

@@ -3,6 +3,10 @@ name: Build pull request
 on:
   pull_request:
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number }}
+  cancel-in-progress: true
+
 jobs:
   build:
     runs-on: ubuntu-latest