[FIX] base: Fix wrong wording for error when archiving a contact with a user still linked to it

Description of the issue/feature this PR addresses and current behavior before PR:
There is a discrepancy in the wording of the error message provided. The error reads that an 'internal user' is linked but really its a 'portal user.'.

Desired behavior after PR is merged:
The wording of the error is clearer, and it now says 'portal user' instead of 'internal user'.

OPW: 2498139

I confirm I have signed the CLA and read the PR guidelines at www.odoo.com/submit-pr

closes odoo/odoo#69916

X-original-commit: cdd94cdd
Signed-off-by: Simon Goffin (sig) <sig@openerp.com>
Signed-off-by: Kamen Zhekov <kzhekov@users.noreply.github.com>