[DOC] Tweaks for StringIO.closed_read? #449

Job	Run time
ruby-versions / Generate Ruby versions	5s
windows-latest 3.2	1m 10s
windows-latest 3.1	1m 8s
windows-latest 3.3	1m 36s
windows-latest 2.7	1m 35s
windows-latest 3.0	1m 2s
windows-latest mswin	1m 18s
windows-latest 3.4	58s
windows-latest mingw	1m 2s
windows-latest jruby-head	1m 35s
	11m 29s

Provide feedback