Add GitHub Actions workflow to run tests with code coverage

.github/workflows/test.yml

@@ -0,0 +1,27 @@
+# .github/workflows/php.yml
+
+name: PHPUnit with coverage
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: '8.1'
+      - name: Install dependencies
+        run: composer install
+      - name: Run tests with coverage
+        run: vendor/bin/phpunit --coverage-text --coverage-clover=coverage.xml
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v2
+        with:
+          files: coverage.xml