Fix wrong namesppace for RuntimeException

Prev code caused 
Instantiated class                                                   
         Endereco\Shopware6ClientStore\Installer\RuntimeException not found.  
         💡 Learn more at https://phpstan.org/user-guide/discovering-symbols  
with phpstan. So i explicitely importet the RuntimeException with use.

src/Installer/PluginLifecycle.php

@@ -5,6 +5,7 @@
 namespace Endereco\Shopware6Client\Installer;
 
 use Doctrine\DBAL\Connection;
+use RuntimeException;
 use Shopware\Core\Framework\Plugin\Context\InstallContext;
 use Shopware\Core\Framework\Plugin\Context\UninstallContext;
 use Shopware\Core\Framework\Plugin\Context\UpdateContext;