That’s because SQLAlchemy filters are one of the few places where == False actually makes sense. Everywhere else you should not use it.
Add a # noqa comment to the line and be done with it.
Or you can use sqlalchemy.sql.expression.false:
from sqlalchemy.sql.expression import false
TestCase.obsoleted == false()
where false() returns the right value for your session SQL dialect. There is a matching sqlalchemy.expression.true.