[rubygems/rubygems] Update main.yml.tt

https://github.com/rubygems/rubygems/commit/3260173c59

lib/bundler/templates/newgem/github/workflows/main.yml.tt

@@ -14,7 +14,7 @@ jobs:
     strategy:
       matrix:
         ruby:
-          - '<%= RUBY_VERSION.split(".").take(2).join(".") %>'
+          - '<%= RUBY_VERSION %>'
 
     steps:
     - uses: actions/checkout@v2