Example changes that show the impact of alter the base_fields attribute.

[Antoliny]

There is an example of the impact of changing the attribute of base_fields in the ​forms api document.

According to the above document, I think we need to show the impact on subsequent ContactForm when we change the base_fields attribute as an example of ContactForm.

>>> f.base_fields["subject"].label_suffix = "?"
>>> another_f = ContactForm(auto_id=False)
>>> another_f.as_div().split("</div>")[0]
'<div><label for="id_subject">Subject?</label><input type="text" name="subject" maxlength="100" required id="id_subject">'

[Antoliny]

​PR

[Sarah Boyce <42296566+sarahboyce@…>]

In 738e0601:

Fixed #35871 -- Corrected example on altering the base_fields attribute in forms docs.

[Sarah Boyce <42296566+sarahboyce@…>]

In a0ea554d:

[5.1.x] Fixed #35871 -- Corrected example on altering the base_fields attribute in forms docs.

Backport of 738e0601d597d4b6bee0000f645994495af984d8 from main.