update serializers Field arguments to be named-only

[asottile-sentry]

Bug report

basically apply the changes encode/django-rest-framework#7632 but to the stubs

What's wrong

I'm attempting to upgrade drf -- and I'd have a lot more confidence if the type checker could help me find the places I'm missing

How is that should be

see above

System information

• OS:
• python version: n/a
• django version: n/a
• mypy version: n/a
• django-stubs version: n/a

[intgr]

Turns out some positional arguments remain. #491