fix migrate guest user being triggered on mixed case email

Signed-off-by: Robin Appelman <[email protected]>

lib/Hooks.php

@@ -221,7 +221,7 @@ public function handleFirstLogin(GenericEvent $event): void {
 			return;
 		}
 
-		if ($email === $user->getUID()) {
+		if (strtolower($email) === strtolower($user->getUID())) {
 			// This is the guest user, logging in for the very first time
 			return;
 		}