run pipeline with specific php version

Signed-off-by: Dominik Meyer <kinimodmeyer@gmail.com>

Author: kinimodmeyer

.github/workflows/ci.yml

@@ -9,6 +9,10 @@ jobs:
         php-versions: ['7.3', '7.4']
     steps:
       - uses: actions/checkout@v2
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php-versions }}
       - name: Install dependencies
         run: composer install
       - name: Run PSR check on src