Change debug test workaround to use ENV RUBY_DEBUG_TEST_UI #4000

Job	Run time
lint	13s
Debug compatibility test	5m 47s
ruby-versions / Generate Ruby versions	4s
rake test 2.7 (latest reline)	1m 33s
vterm-yamatanooroti 2.7 (latest reline)	1m 6s
rake test 2.7	1m 27s
vterm-yamatanooroti 2.7	1m 5s
rake test 3.0 (latest reline)	1m 27s
vterm-yamatanooroti 3.0 (latest reline)	54s
rake test 3.0	1m 26s
vterm-yamatanooroti 3.0	53s
rake test 3.1 (latest reline)	1m 26s
vterm-yamatanooroti 3.1 (latest reline)	54s
rake test 3.1	1m 24s
vterm-yamatanooroti 3.1	54s
rake test 3.2 (latest reline)	1m 25s
vterm-yamatanooroti 3.2 (latest reline)	54s
rake test 3.2	1m 27s
vterm-yamatanooroti 3.2	54s
rake test 3.3 (latest reline)	1m 22s
vterm-yamatanooroti 3.3 (latest reline)	57s
rake test 3.3	1m 24s
vterm-yamatanooroti 3.3	55s
rake test head (latest reline)	1m 42s
vterm-yamatanooroti head (latest reline)	58s
rake test head	2m 6s
vterm-yamatanooroti head	58s
rake test truffleruby-head (latest reline)	2m 44s
rake test truffleruby-head	2m 42s
	41m 1s

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