add GitHub Actions workflow for tests

.github/workflows/php-tests.yml

@@ -0,0 +1,34 @@
+name: Run Tests
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        php-version: [ 8.0, 8.1, 8.2 ]
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Set up PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php-version }}
+          extensions: mbstring, dom, pdo, pdo_mysql
+          coverage: none
+
+      - name: Install dependencies
+        run: composer install --prefer-dist --no-progress --no-suggest
+
+      - name: Run tests
+        run: ./vendor/bin/phpunit --testdox