[DOC] Tweaks for StringIO.closed_write? #444

Job	Run time
ruby-versions / Generate Ruby versions	5s
windows-latest 2.7	1m 39s
windows-latest 3.2	1m 23s
windows-latest 3.1	1m 6s
windows-latest 3.4	1m 24s
windows-latest 3.0	1m 7s
windows-latest mingw	1m 3s
windows-latest jruby-head	1m 44s
windows-latest mswin	2m 5s
windows-latest 3.3	1m 17s
	12m 53s

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