Since commit 2ca11234 (MDEV-26217)
the function trx_t::commit(std::vector<pfs_os_file_t>&)
holds exclusive lock_sys.latch while invoking fil_delete_tablespace(),
which in turn may wait for change buffer tree latches in
ibuf_delete_for_discarded_space().

ibuf_insert_low(): If a shared lock_sys.latch cannot be acquired
without waiting, refuse to buffer the insert. In this way, a
deadlock with a DDL operation will be avoided.

ibuf_insert_to_index_page(), ibuf_delete(): Remove redundant calls to
record locking. In ibuf_insert_low() we already ensured that no record
locks existed on the page. No locks can be added before the buffered
changes have been merged.