Fix IntegrationTestCase #2303

Job	Run time
ruby-versions / Generate Ruby versions	2s
rake test 2.7 (latest reline)	57s
rake test 2.7	43s
rake test 3.0 (latest reline)	27s
rake test 3.0	26s
rake test 3.1 (latest reline)	28s
rake test 3.1	29s
rake test 3.2 (latest reline)	29s
rake test 3.2	32s
rake test head (latest reline)	33s
rake test head	32s
rake test truffleruby-head (latest reline)	7m 50s
rake test truffleruby-head	6m 53s
vterm-yamatanooroti 2.7 (latest reline)	1m 26s
vterm-yamatanooroti 2.7	1m 10s
vterm-yamatanooroti 3.0 (latest reline)	43s
vterm-yamatanooroti 3.0	44s
vterm-yamatanooroti 3.1 (latest reline)	1m 4s
vterm-yamatanooroti 3.1	45s
vterm-yamatanooroti 3.2 (latest reline)	47s
vterm-yamatanooroti 3.2	46s
vterm-yamatanooroti head (latest reline)	51s
vterm-yamatanooroti head	48s
	29m 25s

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