Disable recents background color test when using blurred background

This test fails when using a blurred background on the glanceable hub,
as we no longer propagate the background color to wmshell. Disable the
test to avoid blocking flag propagation.

Bug: 389788272
Flag: com.android.systemui.glanceable_hub_blurred_background
Test: atest WMShellTest
Change-Id: Ia5b21f60d2807d3e31012388ad8dcc639b98403a