DO NOT MERGE: Mark FrameRateOverrideTest#testAppBackpressure as Ignore

This test became flaky on aosp

Bug: 350443755
Test:presubmit
Flag: EXEMPT bugfix
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:5f35b73c267b77ef49ddb74379f347a2c99bbb3e)
Merged-In: I239845582c1c12307c7d74cbc12183b560fec83a
Change-Id: I239845582c1c12307c7d74cbc12183b560fec83a