[DOC] Tweaks for StringIO#close_write #461

Job	Run time
ruby-versions / Generate Ruby versions	5s
windows-latest 3.3	1m 38s
windows-latest 2.7	1m 32s
windows-latest 3.1	1m 2s
windows-latest jruby-head	1m 35s
windows-latest 3.4	1m 4s
windows-latest 3.2	1m 6s
windows-latest mingw	1m 3s
windows-latest mswin	1m 49s
windows-latest 3.0	59s
	11m 53s

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