Ractor: lock around global variable get/set #589

Job	Run time
cargo test	50s
cargo clippy	34s
make (yjit-bindgen, To fix: use patch in logs, --with-gcc=clang-14 --enable-yjit=dev, /usr/lib/ll...	5m 0s
make (check, RUSTC='rustc +1.58.0', 1.58.0)	8m 59s
make (test-bundled-gems, --enable-yjit=dev)	20m 37s
make (check, --enable-yjit=dev)	13m 35s
make (check, --enable-yjit=dev, --yjit-call-threshold=1 --yjit-verify-ctx --yjit-code-gc, -T --yj...	18m 40s
make (yjit-bench, --enable-yjit=dev, --yjit-stats, true)	9m 31s
YJIT Ubuntu result	2s
	1h 17m 48s

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