Add CI

.github/workflows/code_check.yml

@@ -0,0 +1,23 @@
+name: Code quality check
+
+on: [push, pull_request]
+
+jobs:
+  phpunit:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Set up PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: 7.4
+
+      - name: Install dependencies
+        run: composer install --prefer-dist --no-progress --no-suggest
+
+      - name: Run PHPUnit
+        run: vendor/bin/phpunit
+