Add GitHub actions CI

.github/workflows/ci.yml

@@ -0,0 +1,36 @@
+name: CI
+
+on:
+  push:
+    branches: [ main, master ]
+  pull_request:
+    branches: [ '**' ]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        ruby-version:
+          - '2.2'
+          - '2.3'
+          - '2.4'
+          - '2.7'
+          - '3.0'
+          - '3.1' 
+          - '3.2'
+          - '3.3'
+          - 'head'
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Ruby ${{ matrix.ruby-version }}
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby-version }}
+          bundler-cache: true  # runs 'bundle install' and caches installed gems automatically
+
+      - name: Run tests
+        run: bundle exec rake