Try to add PHPUnit

Author: arokettu

.github/workflows/ci.yml

@@ -0,0 +1,14 @@
+name: CI
+
+on: [push]
+
+jobs:
+  build-test:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+      - uses: php-actions/composer@v6
+      - uses: php-actions/phpunit@v4
+        with:
+          vendored_phpunit_path: 'vendor/bin/phpunit'