[DOC] Tweaks for StringIO#close_write #500

Job	Run time
ruby-versions / Generate Ruby versions	5s
ubuntu-24.04 3.4	19s
ubuntu-24.04 3.1	17s
ubuntu-24.04 2.7	42s
ubuntu-24.04 3.0	17s
ubuntu-24.04 3.2	19s
ubuntu-22.04 2.7	46s
ubuntu-24.04 debug	20s
ubuntu-24.04 3.3	23s
ubuntu-24.04 head	12s
ubuntu-24.04 truffleruby-head	22s
ubuntu-22.04 3.4	23s
ubuntu-22.04 3.0	17s
ubuntu-24.04 jruby-head	1m 3s
ubuntu-22.04 head	16s
ubuntu-22.04 debug	23s
ubuntu-22.04 3.3	19s
ubuntu-22.04 3.1	21s
ubuntu-22.04 3.2	18s
ubuntu-22.04 jruby-head	1m 6s
ubuntu-22.04 truffleruby-head	23s
	8m 51s

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