CI: macos runners: use macos-15/macos-15-intel (#7935) #8661

Job	Run time
build-compiler (ubuntu-24.04, ocaml-variants.5.3.0+options,ocaml-option-static, true, true, linux...	5m 7s
build-compiler (windows-2022, 5.3.0, true, win32-x64, x86_64-pc-windows-gnu)	3m 42s
build-compiler (macos-15, 5.3.0, true, darwin-arm64, aarch64-apple-darwin)	26m 17s
build-compiler (ubuntu-24.04-arm, ocaml-variants.5.3.0+options,ocaml-option-static, true, true, t...	6m 36s
build-compiler (macos-15-intel, 5.3.0, true, darwin-x64, x86_64-apple-darwin)	31m 2s
build-compiler (ubuntu-24.04, ocaml-variants.4.14.2+options,ocaml-option-static, linux-x64, x86_6...	19m 14s
api-docs	5s
pkg-pr-new	53s
test-integration-rewatch (macos-15-intel)	1m 43s
test-integration-rewatch (macos-15)	56s
test-integration-rewatch (ubuntu-24.04-arm)	52s
test-integration-rewatch (ubuntu-24.04)	54s
test-integration-rewatch (windows-2022)	1m 54s
test-installation-pnpm (ubuntu-24.04-arm)	16s
test-installation-pnpm (macos-15-intel)	23s
test-installation-pnpm (ubuntu-24.04)	12s
test-installation-pnpm (macos-15)	17s
test-installation-pnpm (windows-2022)	40s
test-installation-npm (ubuntu-24.04)	15s
test-installation-npm (macos-15)	22s
test-installation-npm (ubuntu-24.04-arm)	18s
test-installation-npm (windows-2022)	52s
test-installation-npm (macos-15-intel)	32s
publish	0s
	1h 43m 22s

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