Temporarily disable failing tests in IconTest from Ravenwood

New code in Icon.java is using DesktopExperienceFlags, which seems
to not be working in Ravenwood yet.

Temporarily disable them to fix b/431981370, while a fix forward is
investigated.

Fixes: 431981370
Flag: EXEMPT test exclusion
Test: atest FrameworksCoreTestsRavenwood
Change-Id: I7bb8944e61e40e2b15c81d242a1c74ab9cf7f9cb