Use newer rb_enc_check from JRuby if available #422

Job	Run time
ruby-versions / Generate Ruby versions	4s
ubuntu-24.04 2.7	36s
ubuntu-24.04 3.0	10s
ubuntu-24.04 3.1	12s
ubuntu-24.04 3.2	9s
ubuntu-24.04 3.3	10s
ubuntu-24.04 3.4	10s
ubuntu-24.04 debug	16s
ubuntu-24.04 head	11s
ubuntu-24.04 jruby-head	55s
ubuntu-24.04 truffleruby-head	24s
ubuntu-22.04 2.7	45s
ubuntu-22.04 3.0	14s
ubuntu-22.04 3.1	16s
ubuntu-22.04 3.2	11s
ubuntu-22.04 3.3	14s
ubuntu-22.04 3.4	13s
ubuntu-22.04 debug	18s
ubuntu-22.04 head	11s
ubuntu-22.04 jruby-head	57s
ubuntu-22.04 truffleruby-head	26s
	7m 2s

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