Use test-unit-ruby-core gem #42

Job	Run time
ruby-versions / Generate Ruby versions	4s
build (2.4 / ubuntu-latest)	14s
build (2.4 / macos-latest)	10s
build (2.5 / ubuntu-latest)	14s
build (2.5 / macos-latest)	10s
build (2.6 / ubuntu-latest)	14s
build (2.6 / macos-latest)	1s
build (2.7 / ubuntu-latest)	13s
build (2.7 / macos-latest)	10s
build (2.7 / windows-latest)	1s
build (3.0 / ubuntu-latest)	13s
build (3.0 / macos-latest)	9s
build (3.0 / windows-latest)	13s
build (3.1 / ubuntu-latest)	11s
build (3.1 / macos-latest)	10s
build (3.1 / windows-latest)	1s
build (3.2 / ubuntu-latest)	10s
build (3.2 / macos-latest)	9s
build (3.2 / windows-latest)	6s
build (head / ubuntu-latest)	7s
build (head / macos-latest)	8s
build (head / windows-latest)	11s
	3m 19s

Provide feedback