Fix debug command in nomultiline mode (#1006) #3964

Job	Run time
lint	9s
Debug compatibility test	5m 52s
ruby-versions / Generate Ruby versions	3s
rake test 2.7 (latest reline)	1m 27s
rake test 2.7	1m 28s
vterm-yamatanooroti 2.7 (latest reline)	1m 9s
rake test 3.0 (latest reline)	1m 28s
vterm-yamatanooroti 2.7	1m 7s
rake test 3.0	1m 17s
vterm-yamatanooroti 3.0 (latest reline)	1m 25s
rake test 3.1 (latest reline)	1m 30s
vterm-yamatanooroti 3.0	52s
rake test 3.1	1m 27s
vterm-yamatanooroti 3.1 (latest reline)	55s
rake test 3.2 (latest reline)	1m 29s
vterm-yamatanooroti 3.1	53s
rake test 3.2	1m 23s
vterm-yamatanooroti 3.2 (latest reline)	54s
rake test 3.3 (latest reline)	1m 26s
vterm-yamatanooroti 3.2	56s
rake test 3.3	1m 23s
vterm-yamatanooroti 3.3 (latest reline)	56s
rake test head (latest reline)	1m 20s
vterm-yamatanooroti 3.3	57s
rake test head	1m 24s
vterm-yamatanooroti head (latest reline)	52s
rake test truffleruby-head (latest reline)	2m 48s
vterm-yamatanooroti head	52s
rake test truffleruby-head	2m 50s
	40m 32s

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