Deactivate isolation spec under non MRI-2.1.2
Deactivate isolation spec under non MRI-2.1.2

The specs check for event sequences that are not consistently
triggerable cross MRI versions. The semantics work under all versions.

backus/mutest,nepalez/mutant,tjchambers/mutant,backus/mutant,backus/mutest,kbrock/mutant