build: workflow concurrency for PR title check (#196)

Author: bestbeforetoday

.github/workflows/pr_title.yml

@@ -4,6 +4,11 @@ on:
   pull_request_target:
     types: [opened, edited, synchronize, reopened]
 
+# Most recent PR change supersedes previous changes.
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 # Default to the minimum read-only token for all jobs.
 permissions:
   contents: read