[ocaml5-issue] Assertion failure during parallel STM Out_channel or Sys tests

[jmid]

The merge of #445 to main triggered an assertion failure and abort on Linux trunk during STM Out_channel test parallel:
https://github.com/ocaml-multicore/multicoretests/actions/runs/8441854686/job/23121952174

random seed: 115742799
generated error fail pass / total     time test name

[ ]    0    0    0    0 / 1000     0.0s STM Out_channel test sequential
[ ]    0    0    0    0 / 1000     0.0s STM Out_channel test sequential (generating)
[✓] 1000    0    0 1000 / 1000     3.7s STM Out_channel test sequential

[02] file runtime/domain.c; line 326 ### Assertion failed: s->running
File "src/io/dune", line 40, characters 7-16:
40 |  (name stm_tests)
            ^^^^^^^^^
(cd _build/default/src/io && ./stm_tests.exe --verbose)
Command got signal ABRT.
[ ]    0    0    0    0 / 1000     0.0s STM Out_channel test parallel

[jmid]

Saw this again in focused tests on #304: Linux 5.3.0+trunk debug - this time on STM Sys test parallel
https://github.com/ocaml-multicore/multicoretests/actions/runs/9131253128/job/25110039250?pr=304

Starting 6-th run

random seed: 357814880
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     9.4s STM Sys test sequential

[ ]    0    0    0    0 / 2500     0.0s STM Sys test parallel
[02] file runtime/domain.c; line 325 ### Assertion failed: s->running
/usr/bin/bash: line 1: 1943510 Aborted                 (core dumped) ./focusedtest.exe -v
[ ]  559    0    0  559 / 2500    50.7s STM Sys test parallel