After previous commits IrActualizer runs only there are at least two modules
in backend input. So to check diagnostics from Actualizer all tests
should contain at least two modules
Diagnostics in test `extendExpectedClassWithAbstractMember.kt` were
changed because there is an exception from IrActualizer caused by
errors from frontend (`ABSTRACT_METHOD_NOT_IMPLEMENTED`), which is
swallowed by this kind of tests