Describe the bug
As a result of #1181, all primary keys are now marked as nullable in ModelSchema, regardless of whether the field is set to nullable or not. I'm not sure why this was done, but I would expect it to defer to the field's own nullable setting instead if for some reason you have a nullable primary key. If the intention was to make this optional for request schemas, I think it should be marked in fields_optional instead in the Meta class.

This is a result of these lines here in fields.py

Versions (please complete the following information):

• Python version: 3.12
• Django version: 5.0.7
• Django-Ninja version: 1.2.1
• Pydantic version: 2.8.2