[FIX] hr_recruitment: synchronize if partner_id changes

Complement to commits:
290465e5
72c62dbf

Prevent synchronization between applicant
and partner if partner information changes.
The partner must be changed to update the applicant.

When someone applies for a job via a platform,
the "generic" email is used to create the applicant.
As a result, all applicants have the same partner.
The different commits and this one ensure that
the partner's email is not overwritten
if we update the applicant's email address.
Because changing the partner's email address
synchronized it with all applicants.
All applicants had the same e-mail address.

opw-3166630

closes odoo/odoo#129091

Signed-off-by: Sofie Gvaladze (sgv) <sgv@odoo.com>