I think it make sense to disable this test; the only possible modification would be to only disable it for macOS <= 10.13.  AFAIK, that's the first version where core dumps were possible.  (Aside: I also saw these core dumps for a long time on 10.13 and never associated it with fork-without-exec in Python code.  Clearly, Apple has not done a good enough job of advertising this change.)

I think it is useful to help users on macOS avoid these problematic idioms, via documentation and defaults.  I think there's no way to predict when the core dumps will happen.  With internal cases, I've seen repeated invocations of the same code only core dump on the first run of the process, and not subsequent ones, for reasons I do not understand.  There seems to be a lot of mystery here, and without some explicit help from Apple, we're just doing our best to guess.