The `/mail/message/post` route wrongly prevent serialization
errors by suppressing any `OperationalError` when writing
on a canned response. This is wrong since the `write` method
does not issue any SQL.
In order to properly prevent serialization errors, the request
is now done with the `SKIP LOCKED` clause.
This is better since the error does not occur, hence:
- No rollback needed
- No need to mute the sql logger
- No need to suppress any exception
closesodoo/odoo#127761
Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>