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.