[peewee] Fix type for field operations

[insideable]

Should fix following mypy and pyright error:

src/main.py:7: error: Too few arguments  [call-arg]
src/main.py:7: note: "not_in" is considered instance variable, to make it class variable use ClassVar[...]
src/main.py:7: error: Argument 1 has incompatible type "list[str]"; expected "CharField"  [arg-type]

[github-actions[bot]]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉