ci: add GitHub Actions workflow

.github/workflows/ci.yml

@@ -0,0 +1,28 @@
+name: ci
+
+on:
+  - pull_request
+  - push
+
+jobs:
+  build:
+    strategy:
+      fail-fast: false
+      matrix:
+        ruby:
+          - 2.7
+          - 3.0
+          - 3.1
+          - 3.2
+          - 3.3
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby }}
+      - name: Install dependencies
+        run: bundle install --jobs $(nproc) --retry 3
+      - name: Run rake
+        run: bundle exec rake