Fix screenshot actions scrolling

We were checking if the actions container *background* was
scrollable (which of course it isn't). Updated to check the
ScrollView correctly.

Bug: 227611566
Fix: 227611566
Test: manual (pulled up wikipedia in french, verified that
scrolling the actions works)

Change-Id: I7b0e779adff879f85bb2482a0c894da79a0ffbcd