Try fixing the flakiness of TaplTestsQuickstep#testSwitchToOverview

The new configuration did not reported to the NexusLauncher activity
when the device rotated to landscape. It seems that the configuration
object of the ActivityClientRecord was unexpectedly updated somewhere,
so the configuration handling was skipped and not reporting to the
activity.

Copy the configuration from mPendingMergedConfiguration vs. directly
assigning the given configuration object reference.

Bug: 185820525
Test: atest NexusLauncherTests:TaplTestsQuickstep
Change-Id: I6768fe86e5c977c32a975562ec058c82d4f9c2fc