Migrate repo to use GitHub Actions (#272)

We are working on consolidating all CI to GitHub Actions.

.github/workflows/ci.yml

@@ -0,0 +1,37 @@
+name: CI
+
+on:
+  push:
+    branches:
+      - 'main'
+  pull_request: {}
+
+defaults:
+  run:
+    shell: bash
+
+jobs:
+  test:
+    name: Test Ruby ${{ matrix.ruby }}
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        ruby:
+          - '2.7'
+          - '3.0'
+          - '3.1'
+          - '3.2'
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby }}
+          bundler-cache: true
+
+      - name: Rubocop
+        run: |
+          bundle exec rubocop
+
+      - name: Spec
+        run: |
+          bundle exec rspec