[#11094] fix(client-python): remove unnecessary audit null check in GroupDTO builder

Author: sunyuhan1998

clients/client-python/gravitino/dto/authorization/group_dto.py

@@ -88,6 +88,4 @@ def with_audit(self, audit: AuditDTO) -> GroupDTO.Builder:
         def build(self) -> GroupDTO:
             if not self._name:
                 raise ValueError("name cannot be null or empty")
-            if self._audit is None:
-                raise ValueError("audit cannot be null")
             return GroupDTO(self._name, self._roles, self._audit)