Django unittest, testing form with disabled field

I'm want to test forms in my django app. I got a form with disabled field.

class SportPitchesForm(forms.ModelForm):
def __init__(self, *args, **kwargs):
    super(SportPitchesForm, self).__init__(*args, **kwargs)
    self.fields["city"].disabled = True
    self.fields['pitch'].required = False

This is my test

    def test_sport_pitches_form(self):
    form = SportPitchesForm(
        data={
            "name": "testpitch",
            "city": 1,
            "location": "ExamplePlace",
            "location_lat": 40.00,
            "location_lon": 50.45,
            "pitch": [1, 2, 3],
        }
    )
    print(form.errors)
    self.assertTrue(form.is_valid())

I got this error:

<ul class="errorlist"><li>city<ul class="errorlist"><li>This field is required.</li></ul></li></ul>

When field is enabled my test works.