Fix minor layout issue on Django 3.2

[dmptrluke]

#33 by @kavdev fixed a layout issue with django-markdownfield in newer versions of Django, but has caused a minor regression in Django 3.2.

This issue isn't as impactful as the issue the original code had in newer versions, so I don't want to revert the change, but I would like to find a solution to fix the regression on 3.2 while it's still supported.