Add gd

Author: casperbakker

.github/workflows/phpunit.yml

@@ -18,7 +18,7 @@ jobs:
       uses: shivammathur/setup-php@v1
       with:
         php-version: ${{ matrix.php-versions }}
-        extensions: mbstring
+        extensions: mbstring, gd
 
     - name: Validate composer.json
       run: composer validate