Reduce boilerplate code in RubyLexTest #2198

Job	Run time
ruby-versions / Generate Ruby versions	2s
rake test 2.7 (latest reline)	41s
rake test 2.7	48s
rake test 3.0 (latest reline)	27s
rake test 3.0	26s
rake test 3.1 (latest reline)	31s
rake test 3.1	28s
rake test 3.2 (latest reline)	33s
rake test 3.2	29s
rake test head (latest reline)	28s
rake test head	56s
rake test truffleruby-head (latest reline)	6m 5s
rake test truffleruby-head	5m 18s
vterm-yamatanooroti 2.7 (latest reline)	1m 10s
vterm-yamatanooroti 2.7	1m 24s
vterm-yamatanooroti 3.0 (latest reline)	42s
vterm-yamatanooroti 3.0	35s
vterm-yamatanooroti 3.1 (latest reline)	40s
vterm-yamatanooroti 3.1	38s
vterm-yamatanooroti 3.2 (latest reline)	42s
vterm-yamatanooroti 3.2	36s
vterm-yamatanooroti head (latest reline)	38s
vterm-yamatanooroti head	38s
	24m 55s

Provide feedback