Add GitHub actions workflow for CI

.github/workflows/build-and-test.yml

@@ -0,0 +1,19 @@
+name: Ruby
+
+on:
+  push:
+    branches: [ main ]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@477b21f02be01bcb8030d50f37cfec92bfa615b6
+        with:
+          bundler-cache: true
+      - name: Install dependencies
+        run: bundle install
+      - name: Run tests
+        run: bundle exec rake