Speed up CI by splitting benchmark tests into separate jobs #1487

Job	Run time
benchmark-default (ruby)	11m 23s
benchmark-default (truffleruby)	25s
benchmark-default (head)	11m 15s
test (head)	11s
test (truffleruby)	17s
test (ruby)	10s
benchmark-run-once	1m 36s
benchmark-ractor (head)	12m 19s
benchmark-graph	1m 6s
benchmark-ractor-only (head)	46s
benchmark-ractor (ruby)	12m 25s
benchmark-ractor (truffleruby)	16s
benchmark-ractor-only (ruby)	55s
benchmark-ractor-only (truffleruby)	13s
all-tests	4s
	53m 21s

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