Update dependency pytest-asyncio to ^0.21.0

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
pytest-asyncio (changelog)	^0.20.3 -> ^0.21.0

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Release Notes

pytest-dev/pytest-asyncio

v0.21.0: pytest-asyncio 0.21.0

Compare Source

0.21.0 (23-03-19)

• Drop compatibility with pytest 6.1. Pytest-asyncio now depends on pytest 7.0 or newer.
• pytest-asyncio cleans up any stale event loops when setting up and tearing down the
  event_loop fixture. This behavior has been deprecated and pytest-asyncio emits a
  DeprecationWarning when tearing down the event_loop fixture and current event loop
  has not been closed.

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