test: fix stalling future

[mxschmitt]

This fixes:

Task was destroyed but it is pending!
task: <Task pending name='Task-26888' coro=<Page._on_route() running at /root/playwright/playwright/_impl/_page.py:253> wait_for=<Task pending name='Task-26889' coro=<test_page_close_does_not_wait_for_active_route_handlers.<locals>._handler2() running at /root/playwright/tests/async/test_unroute_behavior.py:368> wait_for=<Future pending cb=[<TaskWakeupMethWrapper object at 0xffff6dc6dbb0>()]> cb=[<TaskWakeupMethWrapper object at 0xffff6dc4fb20>()]> cb=[AsyncIOEventEmitter._emit_run.<locals>.callback() at /usr/local/lib/python3.8/dist-packages/pyee/asyncio.py:69]>
Task was destroyed but it is pending!
task: <Task pending name='Task-26889' coro=<test_page_close_does_not_wait_for_active_route_handlers.<locals>._handler2() running at /root/playwright/tests/async/test_unroute_behavior.py:368> wait_for=<Future pending cb=[<TaskWakeupMethWrapper object at 0xffff6dc6dbb0>()]> cb=[<TaskWakeupMethWrapper object at 0xffff6dc4fb20>()]>