Ignore DesktopModeVisualIndicatorTest

Running this test as part of a larger suite causes its background
animations to leak into the next test, causing frequent crashes
of the entire test process.

The test should not run until it can clean up its background threads
and animators in an @After block.

Bug: 419771302
Test: atest WmShellUnitTests
Flag: EXEMPT fixing unit tests
Change-Id: Idf20088fa79dbef92f621d9631872c661f11ea36