macOS

Rename `ractor_safe_set` into `concurrent_set` #654

Job	Run time
make (check, macos-14, --with-jemalloc --with-opt-dir=$(brew --prefix jemalloc))	6m 8s
make (check, macos-13)	9m 36s
make (check, macos-14, --with-gmp)	6m 40s
make (check, macos-15)	6m 15s
make (check, macos-14)	6m 32s
make (test-all, --repeat-count=2, macos-14)	6m 56s
make (check, macos-14, --with-gcc=gcc-14)	8m 15s
make (test-bundled-gems, macos-14)	10m 34s
make (test-bundler-parallel, macos-14)	17m 4s
macOS result	4s
	1h 18m 4s

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