Retired macos-12 and added macos-14 and macos-15 on GitHub Actions #668

Job	Run time
Rust cargo test	34s
make (yjit-bindgen, To fix: use patch in logs, --with-gcc=clang-12 --enable-yjit=dev)	4m 4s
make (check, RUSTC='rustc +1.58.0', 1.58.0)	13m 29s
make (check, --enable-yjit=dev)	19m 54s
make (check, --enable-yjit=dev, --yjit-call-threshold=1 --yjit-verify-ctx)	21m 18s
make (test-all TESTS=--repeat-count=2, --enable-yjit=dev)	30m 38s
make (test-bundled-gems, --enable-yjit=dev)	19m 42s
make (yjit-bench, --enable-yjit=dev, --yjit-stats)	4m 48s
	1h 54m 27s

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