Work hours in a planning do not respect the timezone

Steps to reproduce:
1. Set your computer timezone to 'America/New_York'
2. Install Manufacturing
3. Go to Settings > Manufacturing > Operations and enable Work Orders
4. Go to Settings > Technical > Resource > Working Times and open
   'Standard 40 hours/week' (San Francisco)
5. Edit the timezone to 'America/New_York'
6. Go to Manufacturing > Planning > Planning by Workcenter and trigger
   the day view
7. The work hours are not correct as they do not respect the timezone

Solution:
Add the timezone of the resource's calendar when computing
unavailabilities

opw-2903591

closes odoo/odoo#100538

Related: odoo/enterprise#31913
Signed-off-by: Laurent Stukkens (ltu) <ltu@odoo.com>