[bfops/unity-merge-group]: CI - Run C# test suite on merge_group

Author: bfops

.github/workflows/csharp-test.yml

@@ -5,6 +5,7 @@ on:
     branches:
       - master
   pull_request:
+  merge_group:
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number || format('sha-{0}', github.sha) }}