[ocaml5-issue] Parallel Sys tests cause timeout on trunk - regression

[jmid]

On the CI runs of the merge to main of #504 we saw 12 trunk workflows timing out:

11 workflows timeout in either STM Sys test parallel or STM Sys stress test parallel

• 32bit trunk
• Bytecode trunk
• Cygwin trunk
• FP trunk
• Linux trunk
• Linux trunk debug
• MSVC bytecode trunk
• MSVC trunk
• MinGW trunk
• macOS-ARM64 trunk
• macOS-intel trunk

Bytecode trunk example:
https://github.com/ocaml-multicore/multicoretests/actions/runs/12636815231/job/35209739270

random seed: 527271392
generated error fail pass / total     time test name

[ ]    0    0    0    0 / 1000     0.0s STM Sys test sequential
[ ]    0    0    0    0 / 1000     0.0s STM Sys test sequential (generating)
[✓] 1000    0    0 1000 / 1000     1.8s STM Sys test sequential

[ ]    0    0    0    0 /  200     0.0s STM Sys test parallel
[ ]  118    0    0  118 /  200    58.8s STM Sys test parallel
[✓]  200    0    0  200 /  200    83.0s STM Sys test parallel

[ ]    0    0    0    0 / 1000     0.0s STM Sys stress test parallel
Error: The operation was canceled.

Trunk example:
https://github.com/ocaml-multicore/multicoretests/actions/runs/12636815229/job/35209740033

random seed: 94741838
generated error fail pass / total     time test name

[ ]    0    0    0    0 / 1000     0.0s STM Sys test sequential
[ ]    0    0    0    0 / 1000     0.0s STM Sys test sequential (generating)
[✓] 1000    0    0 1000 / 1000     1.7s STM Sys test sequential

Error: The operation was canceled.

This clearly indicates a regression on parallel Sys testing.

Exceptions:

• The musl workflow instead timed out in STM Out_channel test parallel
• The MinGW bytecode workflow completed as the only trunk one...

[jmid]

This one is easy to recreate locally.

Reported upstream as ocaml/ocaml#13713

[jmid]

Fixed in ocaml/ocaml#13714