Allow defaultLocale to be null for generating common symfony "routeName.{_locale}" routes.

Author: gguseynov

src/Router/AdminRouteGenerator.php

@@ -84,7 +84,7 @@ public function __construct(
         private readonly CacheItemPoolInterface $cache,
         private readonly Filesystem $filesystem,
         private readonly string $buildDir,
-        private readonly string $defaultLocale,
+        private readonly ?string $defaultLocale,
         private readonly iterable $adminRouteControllers = [],
     ) {
     }