gh-151223: fix tsan data races in load global specializations (#151393) #3204

Job	Run time
x86_64-unknown-linux-gnu/gcc	9m 59s
x86_64-unknown-linux-gnu/gcc-free-threading	8m 0s
aarch64-unknown-linux-gnu/gcc	6m 43s
aarch64-apple-darwin/clang	10m 6s
x86_64-apple-darwin/clang	17m 26s
	52m 14s

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