Run test_asyncio_loop on asyncio backend only

Author: davidbrochart

tests/test_eventloop.py

@@ -79,6 +79,7 @@ def do_thing():
 
 
 @windows_skip
+@pytest.mark.parametrize("anyio_backend", ["asyncio"])
 def test_asyncio_loop(kernel):
     def do_thing():
         loop.call_later(0.01, loop.stop)