[DOC] Tweaks for StringIO.new (#144) #496

Job	Run time
ruby-versions / Generate Ruby versions	3s
ubuntu-24.04 2.7	48s
ubuntu-24.04 3.3	20s
ubuntu-24.04 3.0	12s
ubuntu-24.04 3.4	15s
ubuntu-24.04 head	14s
ubuntu-24.04 jruby-head	1m 1s
ubuntu-24.04 debug	24s
ubuntu-24.04 3.2	21s
ubuntu-22.04 2.7	45s
ubuntu-24.04 truffleruby-head	22s
ubuntu-24.04 3.1	14s
ubuntu-22.04 3.2	17s
ubuntu-22.04 3.0	16s
ubuntu-22.04 3.1	21s
ubuntu-22.04 jruby-head	1m 1s
ubuntu-22.04 truffleruby-head	24s
ubuntu-22.04 3.3	20s
ubuntu-22.04 debug	26s
ubuntu-22.04 3.4	18s
ubuntu-22.04 head	17s
	8m 39s

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