[REV] base: revert 9f7f1db5

Revert commit
"[FIX] base: clearer message in case of conflict for no_gap sequences"

This commit changed the error returned in case of SQL conflict for no_gap
sequences, wrongly disabling the automatic retry (service/model.py) in case
of such errors.

Also adds a comment in the dedicated test to ensure the behavior is explained
and the automatic retry isn't broken once again by the same kind of change.

closes odoo/odoo#59904

X-original-commit: f84d728520257262cf0cd86221114c53f8332258
Signed-off-by: Victor Feyens (vfe) <vfe@odoo.com>