Silence pytest warnings about asyncio fixture scope

[mhucka]

In the current version of pytest (8.3.3) with the pytest-asyncio module version 0.24.0, we see the following warnings at the beginning of a pytest run:

warnings.warn(PytestDeprecationWarning(_DEFAULT_FIXTURE_LOOP_SCOPE_UNSET))

..../lib/python3.10/site-packages/pytest_asyncio/plugin.py:208:
PytestDeprecationWarning: The configuration option
"asyncio_default_fixture_loop_scope" is unset. The event loop scope for
asynchronous fixtures will default to the fixture caching scope. Future
versions of pytest-asyncio will default the loop scope for asynchronous
fixtures to function scope. Set the default fixture loop scope explicitly in
order to avoid unexpected behavior in the future. Valid fixture loop scopes
are: "function", "class", "module", "package", "session"

A currently-open issue and discussion over in the pytest-asyncio repo suggests that this is an undesired side-effect of a recent change in pytest-asyncio and is not actually a significant warning. Moreover, the discussion suggests the warning will be removed or changed in the future.

In the meantime, the warning is confusing because it makes it sound like something is wrong. This simple PR silences the warning by adding a suitable pytest init flag to `pyproject.toml'.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 97.83%. Comparing base (2fdee79) to head (8a4ab93). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #6736 +/- ## ======================================= Coverage 97.83% 97.83% ======================================= Files 1077 1077 Lines 92524 92524 ======================================= + Hits 90519 90523 +4 + Misses 2005 2001 -4 ```

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