Change CI runner to specific self-hosted instance

Author: ppagan-ted

.github/workflows/rails_ci_tests.yml

@@ -11,7 +11,7 @@ on:
 
 jobs:
   specs:
-    runs-on: self-hosted
+    runs-on: [ self-hosted, shgar-ubuntu20 ]
     env:
       RAILS_ENV: test
       DATABASE_URL: 'mysql2://127.0.0.1' # shogo82148/actions-setup-mysql@v1 doesn't work with socket