Duplicate COLLATE clause in ALTER TABLE causes OM=>NS replication failure

CREATE TABLE t (a INT);

ALTER TABLE t COLLATE utf8_general_ci, COLLATE utf8_bin;

DROP TABLE t;

Before 10.9.1, specifically before this commit

commit 208addf48444c0a36a2cc16cd2558ae694e905d5

Author: Alexander Barkov

Date:   Tue May 17 12:52:23 2022 +0400

    Main patch MDEV-27896 Wrong result upon `COLLATE latin1_bin CHARACTER SET latin1` on the table or the database level

the above ALTER would succeed quietly, altering the table to the second collation.

Starting from this commit, it fails with ER_CONFLICTING_DECLARATIONS:

mysqltest: At line 2: query 'ALTER TABLE t COLLATE utf8_general_ci, COLLATE utf8_bin' failed: ER_CONFLICTING_DECLARATIONS (1302): Conflicting declarations: 'COLLATE utf8mb3_general_ci' and 'COLLATE utf8mb3_bin'

The error as such is not big news, with CHARACTER SET it happened before; but as with any tightening in behavior, it may cause a replication failure: the statement passes on an old primary, gets written to the binlog, fails on a replica, replication aborts.

I'm setting it to trivial as the workaround is obvious – don't do it, there should be no practical reason to use two COLLATE clauses in the same ALTER.