docs: Update auth error codes link (#1215)

Author: Vinzent03

packages/gotrue/lib/src/types/auth_exception.dart

@@ -14,7 +14,7 @@ class AuthException implements Exception {
   /// In that case [statusCode] will also be null.
   ///
   /// Find the full list of error codes in our documentation.
-  /// https://supabase.com/docs/reference/dart/auth-error-codes
+  /// https://supabase.com/docs/guides/auth/debugging/error-codes
   final String? code;
 
   const AuthException(this.message, {this.statusCode, this.code});