[DOC] Tweaks for StringIO.open (#146) #435

Job	Run time
ruby-versions / Generate Ruby versions	3s
windows-latest 3.0	1m 52s
windows-latest 3.2	1m 41s
windows-latest 3.4	1m 47s
windows-latest 2.7	2m 12s
windows-latest mswin	1m 16s
windows-latest mingw	1m 21s
windows-latest jruby-head	2m 31s
windows-latest 3.3	1m 49s
windows-latest 3.1	2m 13s
	16m 45s

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