Django removes my custom html attributes from option tag

Question

I am trying to add custom data-* attributes to the option tag in a select element. I have my custom template (widget) which is used by Django, but it seems like Django removes my custom attributes. somewhere in further steps

My custom option template:
widgets/tree_option_template.html

<option value="{{ widget.attrs.lft|stringformat:'s' }}"
    data-test="test"
>{{ widget.label }} - {{ widget.attrs.rght|stringformat:'s' }}</option>

Custom widget:

class MultiChoiceFilterWidget(forms.SelectMultiple):
    """
    TODO.
    Based on FilteredSelectMultiple
    """

    option_inherits_attrs = True
    option_template_name = "widgets/tree_option_template.html"
    ...

Usage in admin.py:

class UserAdminForm(forms.ModelForm):
    class Meta:
        model = User
        fields = "__all__"

    read_projects = CustomTreeNodeMultipleChoiceField(
        queryset=Project.objects.filter(disabled=False),
        required=False,
        widget=MultiChoiceFilterWidget(verbose_name="Projects", is_stacked=False),
    )

When I am changing e.g. value attribute then it changes in DOM as well but my custom attributes are not available in HTML:
As we can see there is no data-test attribute...

Any idea why my custom tags are not visible in HTML?
Thanks!