requirements.txt is ignored when Pipfile exists

[CorralPeltzer]

Package manage/ecosystem
pip
What you expected to see, versus what you actually saw
My repo (https://github.com/CorralPeltzer/newTrackon) has both requirements.txt and Pipfile with only top level dependencies.

According to the configuration, Dependabot is monitoring both files. However, on PRs it only updates Pipfile, see CorralPeltzer/newTrackon#106.

This was reported in dependabot/feedback#435, but the proposed solution (generating requirements.txt, with Pipenv, which adds all transitive dependencies) is not what I'd like to have.