Limit the parallelism in julia-tests.yml

[odow]

Limit the number of parallel tests in HiGHS.jl to 1 to avoid issues with thread management on macOS and Linux.

Discussed with @galabovaa via email

Hi Oscar,

We are having failures on latest, I think due to the number of tests run in parallel

https://github.com/jump-dev/HiGHS.jl/blob/7345ec0de7b722e5cc9f0e91eb9a22765eabd68c/test/runtests.jl#L10

It is hardcoded here so I can't overwrite it in the HiGHS test workflow. It appears that often, but not always, some thread limit on the CI is hit.

See https://github.com/ERGO-Code/HiGHS/actions/runs/25165647977/job/73773337968

Could you please lower that to 2 or 1 maybe?

Thank you,
Ivet

I fixed the hard-coded --jobs=4 in HiGHS.jl: jump-dev/HiGHS.jl#339, so now we can mess with it here.

I don't know if this is a thing we should fix in ERGO-Code/HiGHS, where we more gracefully catch situations in which the number of threads is oversubscribed, or if we should fix this in HiGHS.jl by limiting the number of threads based on how many parallel jobs there are.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.31%. Comparing base (8d1d5db) to head (da02a90).
⚠️ Report is 9 commits behind head on latest.

Additional details and impacted files

@@           Coverage Diff           @@
##           latest    #2998   +/-   ##
=======================================
  Coverage   81.31%   81.31%           
=======================================
  Files         359      359           
  Lines       88852    88852           
=======================================
+ Hits        72253    72254    +1     
+ Misses      16599    16598    -1     

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