Fix test setup in AccessibilityQsShortcutsRepositoryImplForDeviceTest

Root cause: The "launch" was not executed immediately because we were
using the StandardTestDispatcher

With using the SysUI test framework - Kosmos, which by default using
UnconfinedTestDispatcher, the "launch" runs immediately so the test is
setup correctly.

Bug: 438549827
Test: atest (with enable and disable the flag)
Flag: EXEMPT test only
Change-Id: I6eaaf2e0ccb43c694d40b7398fa96b363ed9b7d9