Deprecate macos-12 test in CI #1191

Job	Run time
ruby-versions / Generate Ruby versions	3s
ubuntu-22.04 2.7	48s
ubuntu-22.04 3.0	17s
ubuntu-22.04 3.1	21s
ubuntu-22.04 3.2	18s
ubuntu-22.04 3.3	26s
ubuntu-22.04 head	22s
ubuntu-20.04 2.7	45s
ubuntu-20.04 3.0	21s
ubuntu-20.04 3.1	17s
ubuntu-20.04 3.2	18s
ubuntu-20.04 3.3	17s
ubuntu-20.04 head	17s
macos-14 2.7	46s
macos-14 3.0	24s
macos-14 3.1	23s
macos-14 3.2	23s
macos-14 3.3	23s
macos-14 head	20s
macos-13 2.7	1m 46s
macos-13 3.0	33s
macos-13 3.1	37s
macos-13 3.2	33s
macos-13 3.3	38s
macos-13 head	41s
windows-latest 2.7	4m 22s
windows-latest 3.0	2m 53s
windows-latest 3.1	2m 30s
windows-latest 3.2	2m 55s
windows-latest 3.3	2m 27s
windows-latest ucrt	2m 20s
windows-latest mswin	1m 52s
ubuntu-20.04 jruby	1m 19s
ubuntu-20.04 jruby-head	1m 23s
	34m 18s

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