code: def get_last_modified_date(
              self,
              bucket: str,
              key: str,
      ) -> datetime.datetime:
          
          blob_obj = self._get_blob_obj(bucket, key)
          return blob_obj.updated
docs: Retrieves last modified date for a given key in a given bucket.
          :param bucket: the bucket the object resides in.
          :param key: the key of the object for which the last modified date is being retrieved.
          :return: the last modified date