Synchronize RootWindowContainerTests

There were a few failures that seem to be threading issues.
Specifically, IndexOutOfBounds within a for loop that was iterating the
size of the ArrayList and ArrayMap index failure. RootWindowContainerTests
calls into methods in WM that assume the WM lock is already held. Ensure
testSetDisplayOverrideConfigurationIfNeeded is synchronized.

Test: RootWindowContainerTests#testSetDisplayOverrideConfigurationIfNeeded
Change-Id: I5003fc4a59baae4990a1464dbbc85b0938312994
Fixes: 78349285