Unable to run tests under `pytest-asyncio` 0.19.0

[Jonathan LEI]

Running test cases under pytest-asyncio results in errors (taking one failed test as example):

FAILED tests/DefaultInterestRateModel_test.py::test_borrow_rates - AttributeError: 'coroutine' object has no attribute 'model'

Reverting pytest-asyncio 0.18.0 fixes this. We need to figure out what is broken so we can adapt.

[Jonathan LEI]

Looks like it's caused by:

pytest-dev/pytest-asyncio#380