Use test-unit-ruby-core gem #154

Job	Run time
ruby-versions / Generate Ruby versions	9s
ubuntu-20.04 2.5	1m 48s
ubuntu-20.04 2.6	2m 3s
ubuntu-20.04 2.7	1m 14s
ubuntu-20.04 3.0	29s
ubuntu-20.04 3.1	36s
ubuntu-20.04 3.2	33s
ubuntu-20.04 head	31s
ubuntu-20.04 jruby	1m 27s
ubuntu-20.04 jruby-head	1m 38s
ubuntu-20.04 truffleruby	53s
ubuntu-20.04 truffleruby-head	1m 1s
ubuntu-22.04 2.5	1m 9s
ubuntu-22.04 2.6	2m 52s
ubuntu-22.04 2.7	1m 16s
ubuntu-22.04 3.0	43s
ubuntu-22.04 3.1	36s
ubuntu-22.04 3.2	21s
ubuntu-22.04 head	31s
ubuntu-22.04 jruby	1m 52s
ubuntu-22.04 jruby-head	2m 33s
ubuntu-22.04 truffleruby	50s
ubuntu-22.04 truffleruby-head	1m 21s
macos-11 2.5	2m 28s
macos-11 2.6	2m 14s
macos-11 2.7	3m 13s
macos-11 3.0	38s
macos-11 3.1	42s
macos-11 3.2	46s
macos-11 head	40s
macos-11 jruby	1m 28s
macos-11 jruby-head	1m 32s
macos-11 truffleruby	1m 15s
macos-11 truffleruby-head	1m 27s
macos-12 2.5	2m 34s
macos-12 2.6	2m 15s
macos-12 2.7	2m 16s
macos-12 3.0	43s
macos-12 3.1	47s
macos-12 3.2	45s
macos-12 head	54s
macos-12 jruby	1m 41s
macos-12 jruby-head	2m 2s
macos-12 truffleruby	1m 21s
macos-12 truffleruby-head	1m 37s
windows-latest 2.5	3m 10s
windows-latest 2.6	7m 31s
windows-latest 2.7	3m 11s
windows-latest 3.0	2m 7s
windows-latest 3.1	1m 55s
windows-latest 3.2	3m 55s
windows-latest head	1m 45s
ubuntu-latest jruby-9.2	1m 46s
ubuntu-latest jruby-9.3	1m 26s
	1h 26m 30s

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