Migrate CI from Travis to GitHub Actions

Author: mishina2228

.github/workflows/ci.yml

@@ -0,0 +1,23 @@
+name: CI
+on:
+  pull_request:
+  push: { branches: master }
+permissions:
+  contents: read
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        ruby-version: ['2.3', '2.4', '2.5', '2.6', '2.7', '3.0', '3.1', 'ruby-head']
+    continue-on-error: ${{ matrix.ruby-version == 'ruby-head' }}
+    steps:
+      - uses: actions/checkout@v3
+      - 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 test