www/py-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 2a61802fbd9a0563517335166ccacddd662a086b)