Add macos platform for JRuby CI

Author: headius

.github/workflows/ci.yml

@@ -34,6 +34,7 @@ jobs:
           - { os: ubuntu-latest  , ruby: 3.4, env: "JSON_DEBUG=1" }
           - { os: macos-13, ruby: 3.4 }
           - { os: windows-latest , ruby: mswin     } # ruby/ruby windows CI
+          - { os: macos-latest  , ruby: jruby-9.4 } # Ruby 3.1
           - { os: ubuntu-latest  , ruby: jruby-9.4 } # Ruby 3.1
           - { os: macos-latest   , ruby: truffleruby-head }
           - { os: ubuntu-latest  , ruby: truffleruby-head }