ci: add concurrency group to ci-push workflow (#426)

Ensures new pushes cancel in-flight CI runs on the same branch.

Ref: vergil-project/vergil-tooling#148

Co-authored-by: Claude <noreply@anthropic.com>

Author: wphillipmoore

.github/workflows/ci-push.yml

@@ -8,6 +8,10 @@ on:
       - 'hotfix/**'
       - 'chore/**'
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 permissions:
   contents: read
   security-events: write