Use test-unit-ruby-core gem #69

Job	Run time
ruby-verions / Generate Ruby versions	4s
build (2.6 / ubuntu-latest)	24s
build (2.6 / macos-latest)	56s
build (2.6 / windows-latest)	1m 54s
build (2.7 / ubuntu-latest)	27s
build (2.7 / macos-latest)	51s
build (2.7 / windows-latest)	1m 43s
build (3.0 / ubuntu-latest)	12s
build (3.0 / macos-latest)	15s
build (3.0 / windows-latest)	47s
build (3.1 / ubuntu-latest)	13s
build (3.1 / macos-latest)	14s
build (3.1 / windows-latest)	2m 10s
build (3.2 / ubuntu-latest)	7s
build (3.2 / macos-latest)	22s
build (3.2 / windows-latest)	2m 30s
build (head / ubuntu-latest)	9s
build (head / macos-latest)	16s
build (head / windows-latest)	53s
build (jruby / ubuntu-latest)	48s
build (jruby / macos-latest)	42s
build (jruby / windows-latest)	3m 22s
build (jruby-head / ubuntu-latest)	43s
build (jruby-head / macos-latest)	41s
build (jruby-head / windows-latest)	2m 8s
build (truffleruby / ubuntu-latest)	34s
build (truffleruby / macos-latest)	50s
build (truffleruby-head / ubuntu-latest)	44s
build (truffleruby-head / macos-latest)	1m 0s
	25m 59s

Provide feedback