Add CI test workflow

.github/workflows/ci.yml

@@ -0,0 +1,30 @@
+name: ci
+
+on:
+  pull_request:
+    branches:
+      - "*"
+  push:
+    branches:
+      - main
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        ruby_version: [2.7.2, 3.0.0]
+    continue-on-error: ${{ endsWith(matrix.ruby, 'head') || matrix.ruby == 'debug' }}
+    # Has to be top level to cache properly
+    env:
+      BUNDLE_JOBS: 4
+      BUNDLE_PATH: "vendor/bundle"
+    steps:
+      - uses: actions/checkout@master
+      - name: Setup Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby_version }}
+          bundler-cache: true
+      - name: Test with Rake
+        run: bundle exec rake