style: reformat src/tests/conftest.py with black

- Formatted `src/tests/conftest.py` using `black` to fix CI formatting failures.
- This change ensures compliance with the repository's strict formatting checks (`poetry run black --check .`).

Co-authored-by: PR0M3TH3AN <[email protected]>

src/tests/conftest.py

@@ -39,9 +39,7 @@ except ImportError:
     has_trio = False
 
 
-@pytest.fixture(
-    params=["asyncio"] + (["trio"] if has_trio else [])
-)
+@pytest.fixture(params=["asyncio"] + (["trio"] if has_trio else []))
 def anyio_backend(request):
     return request.param