Never change the underlying string encoding #399

Job	Run time
ruby-versions / Generate Ruby versions	3s
windows-latest 2.7	3m 54s
windows-latest 3.0	1m 58s
windows-latest 3.1	2m 39s
windows-latest 3.2	2m 7s
windows-latest 3.3	1m 49s
windows-latest 3.4	2m 13s
windows-latest jruby-head	2m 4s
windows-latest mingw	1m 40s
windows-latest mswin	1m 37s
	20m 4s

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