Revert "[CI] Pin action steps that use setup-ocaml to ubuntu 22.04 (#… #921

Job	Run time
install (dev, Ubuntu, ubuntu-latest, 4.09.1)	41m 3s
install (dev, Ubuntu, ubuntu-latest, 4.09.1)	41m 3s
install (dev, macOS, macos-latest, 4.14.2)	32m 46s
install (dev, macOS, macos-latest, 4.14.2)	32m 46s
install (dev, Windows, windows-latest, 4.13.1, -async-proofs-j 1, git+https://github.com/ocaml/oc...	1h 27m 35s
install (dev, Windows, windows-latest, 4.13.1, -async-proofs-j 1, git+https://github.com/ocaml/oc...	1h 27m 35s
install (8.19.0, Ubuntu, ubuntu-latest, 4.09.1)	43m 3s
install (8.19.0, Ubuntu, ubuntu-latest, 4.09.1)	43m 3s
install (8.19.0, macOS, macos-latest, 4.14.2)	36m 35s
install (8.19.0, macOS, macos-latest, 4.14.2)	36m 35s
install (8.19.0, Windows, windows-latest, 4.13.1, -async-proofs-j 1, git+https://github.com/ocaml...	2m 22s
install (8.19.0, Windows, windows-latest, 4.13.1, -async-proofs-j 1, git+https://github.com/ocaml...	1h 32m 5s
install (8.18.0, Ubuntu, ubuntu-latest, 4.09.1)	46m 1s
install (8.18.0, Ubuntu, ubuntu-latest, 4.09.1)	46m 1s
install (8.18.0, macOS, macos-latest, 4.14.2)	37m 25s
install (8.18.0, macOS, macos-latest, 4.14.2)	37m 25s
install (8.18.0, Windows, windows-latest, 4.13.1, -async-proofs-j 1, git+https://github.com/ocaml...	1h 35m 37s
install (8.18.0, Windows, windows-latest, 4.13.1, -async-proofs-j 1, git+https://github.com/ocaml...	1h 35m 37s
	15h 34m 37s

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