[FIX] base: new Mauritanian currency

A new currency has been introduced in Mauritania in 2018:
https://en.wikipedia.org/wiki/Mauritanian_ouguiya



opw-2156411

closes odoo/odoo#41992

X-original-commit: 321fc5b3
Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>