Reduce boilerplate code in RubyLexTest #2200

Job	Run time
ruby-versions / Generate Ruby versions	2s
rake test 2.7 (latest reline)	40s
rake test 2.7	42s
rake test 3.0 (latest reline)	27s
rake test 3.0	34s
rake test 3.1 (latest reline)	43s
rake test 3.1	28s
rake test 3.2 (latest reline)	29s
rake test 3.2	1m 5s
rake test head (latest reline)	26s
rake test head	1m 30s
rake test truffleruby-head (latest reline)	5m 52s
rake test truffleruby-head	5m 31s
vterm-yamatanooroti 2.7 (latest reline)	1m 7s
vterm-yamatanooroti 2.7	1m 7s
vterm-yamatanooroti 3.0 (latest reline)	37s
vterm-yamatanooroti 3.0	54s
vterm-yamatanooroti 3.1 (latest reline)	38s
vterm-yamatanooroti 3.1	1m 0s
vterm-yamatanooroti 3.2 (latest reline)	48s
vterm-yamatanooroti 3.2	38s
vterm-yamatanooroti head (latest reline)	47s
vterm-yamatanooroti head	45s
	26m 50s

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