Remove clang-18 from compilers CI #327

Job	Run time
make (check, --enable-yjit, --yjit)	7m 21s
make (check, --enable-yjit=dev, --yjit-call-threshold=1 --yjit-verify-ctx --yjit-code-gc, -T --yj...	10m 23s
cargo test	37s
YJIT macOS result	4s
	18m 25s

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