Fixed issue in visit_on_duplicate_key_update within a composed expression

Fixed issue in visit_on_duplicate_key_update within a composed expression

Fixed issue in MySQL :meth:`_mysql.Insert.on_duplicate_key_update` which
would render the wrong column name when an expression were used in a VALUES
expression. Pull request courtesy Cristian Sabaila.

Fixes: #7281
Closes: #7285
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/7285
Pull-request-sha: 3e6ad6f2fecc6ae36a10a5a34b5d3d393483edbb

Change-Id: I83377c20eae6358fead9e7e361127938e538a71c
(cherry picked from commit 5740a843ed805d0b066b1e56e8bf3c584c32cf6b)