[FIX] resource: prevent week switch for default schedule

Steps to reproduce:
In Working Times, click on "SWITCH TO 2 WEEKS CALENDAR"
for the default calendar used by the company.

Issue:
A ValidationError appears: 'Attendances can't overlap.'

Cause:
To create a two-week schedule, by default,
we will use attendances provided for the company's default schedule.

When we want to switch from a one-week schedule to a two-week schedule,
we first delete the attendances from the schedule to be modified.
However, if this schedule is the company's default schedule,
it will no longer have the default attendances
that we must use to build the two-week schedule.

So we end up with the two "fictitious" attendances
that are used to delimit the two weeks.

With only these two attendances, the constraint of not having
two overlapping attendances is not respected
(because the two attendances created will be modified
to belong to the same week).

Solution:
Check that the calendar to be modified
is not the default calendar used by the company.

opw-3127337

closes odoo/odoo#112902

X-original-commit: 2f56ffbc
Signed-off-by: Kevin Baptiste <kba@odoo.com>