[FIX] mrp: wrong message construction
[FIX] mrp: wrong message construction

The error message is built from string pieces except one that is a list.
This commit cast this list into a proper string to be able to build the
error message.

closes odoo/odoo#34402

Signed-off-by: Arnold Moyaux <1b212d10e7a24dd6fb14e0bb127a40daacfa07e4@users.noreply.github.com>
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo