Suppress warning when loading rdoc #3936

Job	Run time
lint	21s
Debug compatibility test	5m 44s
ruby-versions / Generate Ruby versions	4s
rake test 2.7 (latest reline)	1m 29s
vterm-yamatanooroti 2.7 (latest reline)	1m 13s
rake test 2.7	1m 31s
vterm-yamatanooroti 2.7	1m 12s
rake test 3.0 (latest reline)	1m 27s
vterm-yamatanooroti 3.0 (latest reline)	53s
rake test 3.0	1m 26s
vterm-yamatanooroti 3.0	52s
rake test 3.1 (latest reline)	1m 24s
vterm-yamatanooroti 3.1 (latest reline)	1m 3s
rake test 3.1	1m 27s
vterm-yamatanooroti 3.1	56s
rake test 3.2 (latest reline)	1m 29s
vterm-yamatanooroti 3.2 (latest reline)	1m 4s
rake test 3.2	1m 28s
vterm-yamatanooroti 3.2	1m 2s
rake test 3.3 (latest reline)	1m 21s
vterm-yamatanooroti 3.3 (latest reline)	52s
rake test 3.3	1m 25s
vterm-yamatanooroti 3.3	58s
rake test head (latest reline)	1m 34s
vterm-yamatanooroti head (latest reline)	55s
rake test head	1m 32s
vterm-yamatanooroti head	59s
rake test truffleruby-head (latest reline)	2m 54s
rake test truffleruby-head	2m 43s
	41m 18s

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