Set the asyncio_default_fixture_loop_scope pytest-asyncio option

I think the fixtures should be within the same scope throughout the
tests, hence session.

pyproject.toml

@@ -87,6 +87,7 @@ warn_unused_ignores = true
 
 [tool.pytest.ini_options]
 addopts = "--no-cov-on-fail --showlocals --strict-markers"
+asyncio_default_fixture_loop_scope = "session"
 asyncio_mode = "auto"
 testpaths = ["tests"]