[DOC] Doc for StringIO.getc (#163) #560

Job	Run time
ruby-versions / Generate Ruby versions	4s
ubuntu-24.04 3.2	24s
ubuntu-24.04 2.7	26s
ubuntu-24.04 3.1	17s
ubuntu-24.04 3.4	16s
ubuntu-24.04 3.0	16s
ubuntu-24.04 debug	21s
ubuntu-24.04 head	18s
ubuntu-24.04 3.3	20s
ubuntu-22.04 3.1	30s
ubuntu-22.04 3.2	22s
ubuntu-24.04 jruby-head	1m 1s
ubuntu-22.04 2.7	27s
ubuntu-22.04 3.0	13s
ubuntu-24.04 truffleruby-head	28s
ubuntu-22.04 3.4	25s
ubuntu-22.04 debug	21s
ubuntu-22.04 head	13s
ubuntu-22.04 truffleruby-head	32s
ubuntu-22.04 3.3	22s
ubuntu-22.04 jruby-head	1m 7s
	8m 43s

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