feat(pytest_asyncio): raise error instead of deprecation warning on async fixtures

[dzhalaevd]

What was wrong?

using @pytest.fixture on async fixtures emitted only a deprecation warning, but plan was to make it an exception

Closes: #1202
Related issue: #1202

How it was fixed?

• Raises pytest.UsageError instead of PytestDeprecationWarning when using @pytest.fixture on async fixtures in strict mode (I'm not really sure about pytest.UsageError because some different func uses usual ValueError)
• Update test cases
• Add changelog entry

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.64%. Comparing base (234b90d) to head (8ea2c92).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1348   +/-   ##
=======================================
  Coverage   93.64%   93.64%           
=======================================
  Files           2        2           
  Lines         409      409           
  Branches       44       44           
=======================================
  Hits          383      383           
  Misses         20       20           
  Partials        6        6           

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