ruby: Fix forking with multiple Ractors #185

Job	Run time
Style check	1m 44s
Build and test (normal, release, MarkSweep)	16m 54s
Build and test (normal, release, StickyImmix)	8m 3s
Build and test (normal, debug, Immix)	6m 48s
Build and test (normal, debug, StickyImmix)	5m 19s
Build and test (normal, debug, MarkSweep)	7m 52s
Build and test (normal, release, Immix)	16m 38s
Build and test (special, debug, StickyImmix, yjit)	5m 5s
Build and test (special, release, StickyImmix, yjit)	8m 26s
Build and test (special, vanilla)	4m 17s
Build and test (normal, release, Immix)	21m 41s
Build and test (normal, release, MarkSweep)	52m 40s
Build and test (normal, debug, StickyImmix)	5m 19s
Build and test (normal, release, StickyImmix)	8m 3s
Build and test (special, release, StickyImmix, yjit)	8m 26s
Build and test (special, debug, StickyImmix, yjit)	5m 5s
Build and test (normal, debug, Immix)	6m 48s
Build and test (normal, debug, MarkSweep)	7m 52s
Style check	1m 44s
Build and test (special, vanilla)	4m 17s
Build and test (normal, release, MarkSweep)	23m 47s
Build and test (special, vanilla)	4m 17s
Build and test (normal, debug, Immix)	6m 48s
Build and test (special, release, StickyImmix, yjit)	8m 26s
Build and test (normal, debug, StickyImmix)	5m 19s
Build and test (special, debug, StickyImmix, yjit)	5m 5s
Build and test (normal, release, StickyImmix)	8m 3s
Build and test (normal, debug, MarkSweep)	7m 52s
Build and test (normal, release, Immix)	21m 41s
Style check	1m 44s
	4h 56m 3s

Provide feedback