Fix failing freeform TDA unit tests in enter-desktop-by-default devices

Devices with the enter_desktop_by_default config enabled were failing
these tests because the tests expects that config to be disabled but was
not explicitly setting up the test to disable it.

Flag: com.android.window.flags.enter_desktop_by_default_on_freeform_displays
Fix: 404227769
Test: atest DesktopTasksControllerTest
Change-Id: Ia5e6e213b08853e7e15ba943beb26f47806c5e8e