[DOC] Doc for StringIO#each_byte #469

Job	Run time
ruby-versions / Generate Ruby versions	5s
windows-latest 3.2	1m 14s
windows-latest 2.7	1m 36s
windows-latest 3.4	1m 9s
windows-latest 3.1	56s
windows-latest 3.3	1m 10s
windows-latest 3.0	1m 4s
windows-latest mingw	59s
windows-latest jruby-head	1m 39s
windows-latest mswin	2m 55s
	12m 47s

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