CI: Update github.ref to github.ref_name

See https://github.blog/changelog/2023-09-13-github-actions-updates-to-github_ref-and-github-ref

.github/workflows/ci.yml

@@ -5,7 +5,7 @@ on:
   pull_request:
 
 concurrency:
-  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref_name }}
   cancel-in-progress: true
 
 jobs:

.github/workflows/sync_class_ref.yml

@@ -11,7 +11,7 @@ on:
 
 # Make sure jobs cannot overlap.
 concurrency:
-  group: classref-sync-ci-master
+  group: classref-sync-ci-${{ github.ref_name }}
   cancel-in-progress: true
 
 jobs: