Bump ocaml/setup-ocaml from 2 to 3 #4612

Job	Run time
macOS 12 (x86_64)	3h 10m 16s
macOS 14 (arm64)	1h 40m 7s
combine-standalone	15s
publish-standalone	14s
publish-standalone (-x86_64)	14s
test-standalone (macos-12)	17s
publish-standalone (-arm64)	24s
test-standalone (macos-13)	20s
test-standalone (macos-14)	10s
test-standalone (macos-latest)	13s
test-standalone (-x86_64, macos-12)	16s
test-standalone (-x86_64, macos-13)	17s
test-standalone (-x86_64, macos-14)	15s
test-standalone (-x86_64, macos-latest)	12s
test-standalone (-arm64, macos-14)	12s
test-standalone (-arm64, macos-latest)	10s
macos-check-all	1s
	4h 53m 53s

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