The upstream report at https://github.com/pytest-dev/pytest-twisted/issues/146 was closed as the additional warning is produced by Twisted. The Twisted fix isn't merged yet.
It looks like the twisted fix has now been merged upstream, does it make sense to apply it as a patch to the Debian twisted patch to solve this bug? The removal of pytest-twisted from testing has caused two packages to have uninstallable build-dependencies in testing, graphql-relay and python-promise
