Do not issue warning when calling set_encoding if string is chilled #447

Job	Run time
ruby-versions / Generate Ruby versions	2s
ubuntu-24.04 2.7	45s
ubuntu-24.04 3.0	23s
ubuntu-24.04 3.1	20s
ubuntu-24.04 3.2	27s
ubuntu-24.04 3.3	22s
ubuntu-24.04 3.4	12s
ubuntu-24.04 debug	31s
ubuntu-24.04 head	21s
ubuntu-24.04 jruby-head	1m 14s
ubuntu-24.04 truffleruby-head	42s
ubuntu-22.04 2.7	49s
ubuntu-22.04 3.0	18s
ubuntu-22.04 3.1	22s
ubuntu-22.04 3.2	23s
ubuntu-22.04 3.3	18s
ubuntu-22.04 3.4	23s
ubuntu-22.04 debug	32s
ubuntu-22.04 head	19s
ubuntu-22.04 jruby-head	1m 27s
ubuntu-22.04 truffleruby-head	46s
	10m 56s

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