I've seen this flake several times; it's not clear from the logs what exactly is failing, or why. Example failing run:
https://api.cirrus-ci.com/v1/task/4968839016873984/logs/unit_test.log

Enabling unawaited_futures for this package might turn up something in a test that's not being awaited, as that's been a source of unit test flake in the past.

/cc @camsim99