Fix errors reported by PHPStan

src/Driver/SymfonyDriver.php

@@ -5,6 +5,7 @@ declare(strict_types=1);
 namespace FriendsOfBehat\SymfonyExtension\Driver;
 
 use Behat\Mink\Driver\BrowserKitDriver;
+use Symfony\Component\BrowserKit\Client;
 use Symfony\Component\HttpKernel\KernelInterface;
 
 final class SymfonyDriver extends BrowserKitDriver
@@ -15,6 +16,16 @@ final class SymfonyDriver extends BrowserKitDriver
      */
     public function __construct(KernelInterface $kernel, string $baseUrl)
     {
-        parent::__construct($kernel->getContainer()->get('test.client'), $baseUrl);
+        $testClient = $kernel->getContainer()->get('test.client');
+
+        if (!$testClient instanceof Client) {
+            throw new \RuntimeException(sprintf(
+                'Expected service "test.client" to be an instance of "%s", got "%s" instead.',
+                Client::class,
+                \is_object($testClient) ? \get_class($testClient) : \gettype($testClient)
+            ));
+        }
+
+        parent::__construct($testClient, $baseUrl);
     }
 }