[ocaml5-issue] Deadlock in 'thread_createtree - with Atomic' on Linux ARM64

[jmid]

We came across a CI run on Linux trunk/5.2 ARM64 which timed out in thread_createtree - with Atomic despite none of the previous tests taking substantial time.

https://ocaml-multicoretests.ci.dev:8100/job/2023-12-12/132004-ci-ocluster-build-19fadd

random seed: 495973125
generated error fail pass / total     time test name

[ ]    0    0    0    0 / 1000     0.0s thread_createtree - with Atomic
[ ]    0    0    0    0 / 1000     0.0s thread_createtree - with Atomic (generating)2023-12-12 18:20.04: Cancelling: Timeout (300.0 minutes)
Job cancelled