[FIX] purchase: no bulgarian for en_GB translation

The translation of purchase.order().notes name (Terms and Conditions) is
wrongly done in bulgarian since 2016
(d14efd56).

opw-2719178

closes odoo/odoo#81993

X-original-commit: b0be51f8
Signed-off-by: Nicolas Lempereur (nle) <nle@odoo.com>