www/py-dj31-django-taggit: Update to 1.5.1

• Add a "do-test" target to make future QA easier.

Changelog since 1.3.0:

https://github.com/jazzband/django-taggit/blob/1.5.1/CHANGELOG.rst

MFH: 2021Q3
(cherry picked from commit ca302be1beafa19e6e70575a8be02e0b086eb3cc)