Ensure that new commits cancel stale CI runs

Author: awalker4

.github/workflows/ci.yaml

@@ -12,6 +12,10 @@ permissions:
   id-token: write
   contents: read
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   test_unit:
     runs-on: ubuntu-latest