Use concurrency to cancel duplicate workflow runs

Docs: https://docs.github.com/en/actions/using-jobs/using-concurrency

.github/workflows/build_pull_request.yml

@@ -5,6 +5,10 @@ on:
       - '**.md'
       - 'app/src/main/res/**/strings.xml'
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number }}
+  cancel-in-progress: true
+
 permissions:
   contents: read