fix test: add phpunit

Author: korelstar

.github/workflows/test.yml

@@ -26,6 +26,7 @@ jobs:
       uses: shivammathur/setup-php@v2
       with:
         php-version: ${{ env.PHP_VERSION }}
+        tools: phpunit:8.5.8
     - name: Install Dependencies
       run: composer install --prefer-dist
     - name: Prepare MySQL database