Run tests on CI

There's a DB matrix so we can plug in running the tests against Postgres
and SQLite later on, but just running MySQL for now.

.github/workflows/main.yml

@@ -0,0 +1,35 @@
+name: Build
+on: [push, pull_request]
+
+jobs:
+  tests:
+    name: Tests
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        ruby-version: [3.2.2]
+        database: [mysql]
+    services:
+      mysql:
+        image: mysql:8.0.31
+        env:
+          MYSQL_ALLOW_EMPTY_PASSWORD: "yes"
+        ports:
+          - 33060:3306
+        options: --health-cmd "mysql -h localhost -e \"select now()\"" --health-interval 1s --health-timeout 5s --health-retries 30
+    env:
+      TARGET_DB: ${{ matrix.database }}
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+      - name: Setup Ruby and install gems
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby-version }}
+          bundler-cache: true
+      - name: Setup test database
+        run: |
+          bin/rails db:setup
+      - name: Run tests
+        run: bin/rails test