Setup GitHub Actions to test and lint

Add a CI action that runs test and lint jobs on pushes and pull requests
to main.

.github/workflows/ci.yml

@@ -0,0 +1,26 @@
+# This workflow uses actions that are not certified by GitHub.  They are
+# provided by a third-party and are governed by separate terms of service,
+# privacy policy, and support documentation.
+#
+# This workflow will install a prebuilt Ruby version, install dependencies, and
+# run tests and linters.
+name: "CI"
+on:
+  push:
+    branches: ["main"]
+  pull_request:
+    branches: ["main"]
+jobs:
+  lint_and_test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+      - name: Install Ruby and gems
+        uses: ruby/setup-ruby@v1
+        with:
+          bundler-cache: true
+          ruby-version: "3.0"
+      - name: Lint with the Standard Ruby style guide and test with RSpec
+        run: rake
+