Mockito: Downgrade Errorprone warning

Ensure that CollectionIncompatibleType isn't fatal until an
upstream fix can be imported.

Bug: 73288226
Bug: 74213384
Test: m javac-check RUN_ERROR_PRONE=true
Change-Id: I46298d6c43afd1a2d1eb064100811697aecaee58
1 file changed