autotests: Make testSlidingPopups quicker

The test waits longer than needed to determine whether effects stopped
playing animations

Before

    Executed in   22.41 secs      fish           external
       usr time  997.42 millis  722.00 micros  996.70 millis
       sys time  744.81 millis   79.00 micros  744.73 millis

After

    Executed in    9.71 secs      fish           external
       usr time  894.42 millis    1.03 millis  893.38 millis
       sys time  689.80 millis    0.11 millis  689.69 millis