[DOC] Tweaks for StringIO#each_line #581

Job	Run time
ruby-versions / Generate Ruby versions	5s
ubuntu-24.04 3.0	20s
ubuntu-24.04 2.7	44s
ubuntu-24.04 3.4	20s
ubuntu-24.04 jruby-head	1m 10s
ubuntu-24.04 3.1	17s
ubuntu-22.04 3.0	18s
ubuntu-24.04 3.2	24s
ubuntu-24.04 debug	25s
ubuntu-22.04 3.1	17s
ubuntu-22.04 3.2	28s
ubuntu-24.04 head	20s
ubuntu-24.04 truffleruby-head	21s
ubuntu-22.04 2.7	43s
ubuntu-24.04 3.3	20s
ubuntu-22.04 debug	30s
ubuntu-22.04 head	14s
ubuntu-22.04 3.4	26s
ubuntu-22.04 jruby-head	1m 13s
ubuntu-22.04 truffleruby-head	35s
ubuntu-22.04 3.3	21s
ruby-versions / Generate Ruby versions	5s
ubuntu-24.04 3.2	24s
ubuntu-24.04 3.3	20s
ubuntu-24.04 3.0	20s
ubuntu-24.04 debug	25s
ubuntu-24.04 head	20s
ubuntu-22.04 2.7	43s
ubuntu-24.04 2.7	44s
ubuntu-22.04 3.0	18s
ubuntu-24.04 jruby-head	1m 10s
ubuntu-24.04 3.1	17s
ubuntu-22.04 3.2	28s
ubuntu-24.04 truffleruby-head	24s
ubuntu-24.04 3.4	20s
ubuntu-22.04 3.3	21s
ubuntu-22.04 3.1	17s
ubuntu-22.04 3.4	26s
ubuntu-22.04 debug	30s
ubuntu-22.04 jruby-head	1m 13s
ubuntu-22.04 head	14s
ubuntu-22.04 truffleruby-head	35s
	19m 45s

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