Improve CI #143

Job	Run time
ruby-versions / Generate Ruby versions	4s
build (2.5 / ubuntu-latest)	31s
build (2.5 / macos-latest)	1m 22s
build (2.6 / ubuntu-latest)	23s
build (2.6 / macos-latest)	1m 14s
build (2.7 / ubuntu-latest)	24s
build (2.7 / macos-latest)	1m 8s
build (3.0 / ubuntu-latest)	13s
build (3.0 / macos-latest)	18s
build (3.1 / ubuntu-latest)	13s
build (3.1 / macos-latest)	14s
build (3.2 / ubuntu-latest)	8s
build (3.2 / macos-latest)	13s
build (head / ubuntu-latest)	15s
build (head / macos-latest)	18s
build (jruby / ubuntu-latest)	44s
build (jruby / macos-latest)	55s
build (jruby-head / ubuntu-latest)	43s
build (jruby-head / macos-latest)	51s
build (truffleruby / ubuntu-latest)	36s
build (truffleruby / macos-latest)	37s
build (truffleruby-head / ubuntu-latest)	47s
build (truffleruby-head / macos-latest)	43s
	12m 54s

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