Flaky test when multithreading

Seen with `-t4,4` on https://github.com/JuliaLang/Distributed.jl/pull/122 ``` Test Failed at D:\a\Distributed.jl\Distributed.jl\test\distributed_exec.jl:252 Expression: testval == 1 Evaluated: 0 == 1 ``` https://github.com/JuliaLang/Distributed.jl/actions/runs/12957263140/job/36145255783?pr=122#step:5:93 Seen on - `t4,4` - [linux](https://github.com/JuliaLang/Distributed.jl/actions/runs/12961673891/job/36157247005?pr=122#step:5:93) - [windows](https://github.com/JuliaLang/Distributed.jl/actions/runs/12961673891/job/36157247311?pr=122#step:5:93) Passed on a re-run