In commit aaef2e1d (MDEV-27058)
we failed to introduce a special copy constructor that would
preserve the "page_zip_des_t::fix" field that only exists there
in order to avoid alignment loss on 64-bit systems.

page_zip_copy_recs(): Invoke the special copy constructor.

The block descriptor corruption causes assertion failures when
running ./mtr --suite=innodb_zip while InnoDB has been built
with UNIV_ZIP_COPY. Normally, calls to page_zip_copy_recs()
occur very rarely on page splits.