Buggy Migrations when `float("nan")` in `Q` objects

[Steven Jin]

When creating a CheckConstraint in the form

class MyModel(Model):
  x = FloatField()
  class Meta:
    constraints = [~CheckConstraint(check=Q(x=float("nan")), name="some constraint")]

This constraint is removed and added back every time python manage.py makemigrations is run. This is because the inherited __eq__ function of Q objects does not take into account the fact that float("nan") != float("nan").

See PR: ​https://github.com/django/django/pull/14706