[FIX] iap: incorrect account selected when buying credits in settings

When buying credits through the "Buy credits" widget of the Settings
app, it would sometimes let you buy credits for an IAP account of a
different company than the active company.

This happened because the context was missing in the request to
`get_credits_url`.

Task #3266189
Ticket #3248662

closes odoo/odoo#137562

Signed-off-by: Francois Georis (fge) <fge@odoo.com>