Add concurrency key to release workflow to prevent overlapping publishes

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: yahonda

.github/workflows/release.yml

@@ -5,6 +5,10 @@ on:
     tags:
       - 'v*'
 
+concurrency:
+  group: release-${{ github.ref }}
+  cancel-in-progress: false
+
 jobs:
   build-cruby:
     name: Build gem (CRuby)