Switch default mode to strict.

- Adds [pytest-trio](https://pypi.org/project/pytest-trio/) to the te…

…st dependencies

- Fixes a bug that caused pytest-asyncio to try to set up async pytest_trio fixtures in strict mode. [pytest-dev#298] (pytest-dev#298)

Maintenance release:

- Fix asyncio auto mode not marking static methods. `pytest-dev#295 <https://github.com/pytest-dev/pytest-asyncio/issues/295>`_
- Fix a compatibility issue with Hypothesis 6.39.0. `pytest-dev#302 <https://github.com/pytest-dev/pytest-asyncio/issues/302>`_

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