[typing] Fix type error when passing Mapped columns to values()

[typing] Fix type error when passing Mapped columns to values()

This adjusts the _DMLOnlyColumnArgument type to be a more
focused _OnlyColumnArgument type where we also add a more tightly
focused coercion, while still allowing ORM attributes to be used
as arguments.

Co-authored-by: Mike Bayer <mike_mp@zzzcomputing.com>
Closes: #13012
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/13012
Pull-request-sha: 5ebb402c686abf1090e5b83e3489dfca4908efdf

Change-Id: I8bbccaf556ec5ecb2f5cfdd2030bcfa4eb5ce125