Never change the underlying string encoding #458

Job	Run time
ruby-versions / Generate Ruby versions	4s
ubuntu-24.04 2.7	46s
ubuntu-24.04 3.0	26s
ubuntu-24.04 3.1	21s
ubuntu-24.04 3.2	25s
ubuntu-24.04 3.3	24s
ubuntu-24.04 3.4	14s
ubuntu-24.04 debug	29s
ubuntu-24.04 head	20s
ubuntu-24.04 jruby-head	1m 7s
ubuntu-24.04 truffleruby-head	41s
ubuntu-22.04 2.7	49s
ubuntu-22.04 3.0	18s
ubuntu-22.04 3.1	19s
ubuntu-22.04 3.2	22s
ubuntu-22.04 3.3	23s
ubuntu-22.04 3.4	21s
ubuntu-22.04 debug	28s
ubuntu-22.04 head	19s
ubuntu-22.04 jruby-head	1m 17s
ubuntu-22.04 truffleruby-head	42s
	10m 35s

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