[DOC] Tweaks for StringIO#fileno (#168) #503

Job	Run time
ruby-versions / Generate Ruby versions	5s
windows-latest 3.1	59s
windows-latest 2.7	1m 41s
windows-latest jruby-head	1m 46s
windows-latest 3.0	1m 3s
windows-latest 3.3	1m 6s
windows-latest mingw	1m 6s
windows-latest 3.4	51s
windows-latest 3.2	1m 5s
windows-latest mswin	1m 24s
	11m 6s

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