Skip nested IRB tests in Ruby Core CI #2344

Job	Run time
ruby-versions / Generate Ruby versions	2s
vterm-yamatanooroti 2.7 (latest reline)	1m 26s
vterm-yamatanooroti 2.7	1m 24s
vterm-yamatanooroti 3.0 (latest reline)	59s
vterm-yamatanooroti 3.0	40s
vterm-yamatanooroti 3.1 (latest reline)	50s
vterm-yamatanooroti 3.1	55s
vterm-yamatanooroti 3.2 (latest reline)	44s
vterm-yamatanooroti 3.2	54s
vterm-yamatanooroti head (latest reline)	46s
vterm-yamatanooroti head	51s
rake test 2.7 (latest reline)	58s
rake test 2.7	44s
rake test 3.0 (latest reline)	29s
rake test 3.0	27s
rake test 3.1 (latest reline)	38s
rake test 3.1	31s
rake test 3.2 (latest reline)	27s
rake test 3.2	40s
rake test head (latest reline)	28s
rake test head	38s
rake test truffleruby-head (latest reline)	6m 51s
rake test truffleruby-head	7m 54s
	30m 16s

Provide feedback