macos

Also setup Java 21 for Windows jruby-head build #440

Job	Run time
ruby-versions / Generate Ruby versions	3s
macos-13 2.7	1m 20s
macos-13 3.0	30s
macos-13 3.1	36s
macos-13 3.2	29s
macos-13 3.3	31s
macos-13 3.4	39s
macos-13 debug	56s
macos-13 head	48s
macos-14 2.7	32s
macos-14 3.0	20s
macos-14 3.1	17s
macos-14 3.2	21s
macos-14 3.3	15s
macos-14 3.4	16s
macos-14 debug	19s
macos-14 head	17s
	8m 29s

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