deskutils/py-todoman: Update to 3.8.0

From ChangeLog: https://todoman.readthedocs.io/en/stable/changelog.html#v3-8-0

• Don't display list if there's only one list (of one list has been specified).
• Fixed several issues when using dates with no times.
• Dropped support for Python 3.4.

PR: 247258
Submitted by: andreas@bilke.org (maintainer)