Load rubygems explicitly for tests of test/irb #3356

Job	Run time
lint	12s
ruby-versions / Generate Ruby versions	3s
rake test 2.7 (latest reline)	1m 11s
vterm-yamatanooroti 2.7 (latest reline)	1m 14s
rake test 2.7	1m 17s
vterm-yamatanooroti 2.7	1m 1s
rake test 3.0 (latest reline)	1m 14s
rake test 3.0	1m 11s
vterm-yamatanooroti 3.0 (latest reline)	51s
rake test 3.1 (latest reline)	1m 15s
vterm-yamatanooroti 3.0	50s
rake test 3.1	1m 18s
vterm-yamatanooroti 3.1 (latest reline)	52s
rake test 3.2 (latest reline)	1m 10s
vterm-yamatanooroti 3.1	1m 19s
rake test 3.2	1m 11s
vterm-yamatanooroti 3.2 (latest reline)	1m 12s
rake test 3.3 (latest reline)	1m 11s
vterm-yamatanooroti 3.2	58s
rake test 3.3	1m 19s
vterm-yamatanooroti 3.3 (latest reline)	57s
rake test head (latest reline)	1m 44s
vterm-yamatanooroti 3.3	1m 14s
rake test head	1m 31s
vterm-yamatanooroti head (latest reline)	1m 4s
rake test truffleruby-head (latest reline)	2m 43s
vterm-yamatanooroti head	1m 17s
rake test truffleruby-head	2m 49s
	34m 8s

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