[DOC] Tweaks for StringIO#pos (#193) #557

Job	Run time
ruby-versions / Generate Ruby versions	4s
windows-latest 2.7	1m 31s
windows-latest 3.0	1m 1s
windows-latest 3.1	1m 2s
windows-latest 3.2	1m 13s
windows-latest 3.3	1m 11s
windows-latest 3.4	50s
windows-latest mingw	1m 11s
windows-latest jruby-head	1m 34s
windows-latest mswin	1m 4s
	10m 41s

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