[DOC] Tweaks for StringIO#closed? (#151) #505

Job	Run time
ruby-versions / Generate Ruby versions	4s
ubuntu-24.04 3.0	18s
ubuntu-24.04 2.7	46s
ubuntu-24.04 3.3	22s
ubuntu-24.04 3.4	12s
ubuntu-24.04 debug	21s
ubuntu-24.04 3.1	16s
ubuntu-24.04 head	16s
ubuntu-24.04 3.2	18s
ubuntu-22.04 3.2	24s
ubuntu-22.04 3.1	22s
ubuntu-22.04 2.7	44s
ubuntu-24.04 truffleruby-head	23s
ubuntu-22.04 3.0	14s
ubuntu-22.04 3.4	16s
ubuntu-24.04 jruby-head	1m 0s
ubuntu-22.04 truffleruby-head	25s
ubuntu-22.04 jruby-head	1m 1s
ubuntu-22.04 3.3	18s
ubuntu-22.04 head	16s
ubuntu-22.04 debug	20s
	8m 36s

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