fix subdomain validation regex

src/Service/Typo3/SubdomainService.php

@@ -23,7 +23,7 @@ class SubdomainService
     public const MAX_SUBDOMAINS_NUMBER = 3;
 
     // Validation regex for subdomains
-    public const RX_VALIDATE_SUBDOMAIN = '/^[A-Za-z0-9](?:[A-Za-z0-9\-]{0,61}[A-Za-z0-9])?$/';
+    public const RX_VALIDATE_SUBDOMAIN = '/^[a-z0-9](?:[a-z0-9\-]{0,61}[a-z0-9])?$/';
 
     public function __construct(
         private readonly SubdomainRepository $subdomainRepository,