Fix IME flicker test in split screen when no layer change was applied

The test in question was using the TRACE_CONFIG_REQUIRE_CHANGES, where at least one layer change was asserted.
With the refactor, there will be no change, if the IME is already showing and requested to be shown again.
By using config.allowNoChange, we don't assert at least one change.

Test: atest WMShellFlickerTestsSplitScreenGroupOther:MultipleShowImeRequestsInSplitScreen
Flag: android.view.inputmethod.refactor_insets_controller
Fix: 355057357
Change-Id: I5dcd12b2a0417039b2a94495417b0e01f8c8f6a3