Move ruby testing to GH Actions & fix linting

.github/workflows/ruby.yml

@@ -0,0 +1,20 @@
+name: Ruby
+on:
+  pull_request:
+
+jobs:
+  ruby_testing:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+        # Due to https://github.com/actions/runner/issues/849, we have to use quotes for '3.0'
+        ruby: ['2.6', '2.7', '3.0', '3.1']
+    runs-on: ${{ matrix.os }}
+    steps:
+    - uses: actions/checkout@v3
+    - uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby }}
+        bundler-cache: true # runs 'bundle install' and caches installed gems automatically
+    - run: bundle exec rake tests