Use test-unit-ruby-core gem #172

Job	Run time
ruby-versions / Generate Ruby versions	3s
ubuntu-20.04 2.3	1m 21s
ubuntu-20.04 2.4	1m 13s
ubuntu-20.04 2.5	1m 15s
ubuntu-20.04 2.6	1m 21s
ubuntu-20.04 2.7	1m 49s
ubuntu-20.04 3.0	34s
ubuntu-20.04 3.1	30s
ubuntu-20.04 3.2	28s
ubuntu-20.04 head	39s
ubuntu-20.04 jruby	1m 41s
ubuntu-20.04 jruby-head	1m 33s
ubuntu-20.04 truffleruby	1m 4s
ubuntu-20.04 truffleruby-head	1m 13s
ubuntu-22.04 2.3	1m 11s
ubuntu-22.04 2.4	1m 25s
ubuntu-22.04 2.5	1m 38s
ubuntu-22.04 2.6	1m 28s
ubuntu-22.04 2.7	2m 20s
ubuntu-22.04 3.0	27s
ubuntu-22.04 3.1	27s
ubuntu-22.04 3.2	35s
ubuntu-22.04 head	36s
ubuntu-22.04 jruby	1m 28s
ubuntu-22.04 jruby-head	1m 53s
ubuntu-22.04 truffleruby	1m 22s
ubuntu-22.04 truffleruby-head	1m 23s
macos-11 2.3	2m 8s
macos-11 2.4	2m 3s
macos-11 2.5	1m 59s
macos-11 2.6	4m 12s
macos-11 2.7	3m 51s
macos-11 3.0	39s
macos-11 3.1	36s
macos-11 3.2	41s
macos-11 head	43s
macos-11 jruby	1m 27s
macos-11 jruby-head	1m 24s
macos-11 truffleruby	1m 38s
macos-11 truffleruby-head	1m 53s
macos-12 2.3	2m 17s
macos-12 2.4	1m 53s
macos-12 2.5	2m 10s
macos-12 2.6	3m 12s
macos-12 2.7	2m 15s
macos-12 3.0	30s
macos-12 3.1	39s
macos-12 3.2	35s
macos-12 head	31s
macos-12 jruby	1m 51s
macos-12 jruby-head	1m 2s
macos-12 truffleruby	1m 46s
macos-12 truffleruby-head	2m 12s
windows-latest 2.3	2m 45s
windows-latest 2.4	3m 54s
windows-latest 2.5	4m 22s
windows-latest 2.6	5m 14s
windows-latest 2.7	4m 37s
windows-latest 3.0	2m 4s
windows-latest 3.1	1m 57s
windows-latest 3.2	3m 5s
windows-latest head	2m 4s
ubuntu-latest jruby-9.1	2m 8s
ubuntu-latest jruby-9.2	2m 10s
ubuntu-latest jruby-9.3	1m 37s
	1h 51m 1s

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