Use sim.make.exec('run_fg', nproc=2)

[akhoubani]

Fixes #31

[codecov[bot]]

Codecov Report

Base: 61.35% // Head: 61.35% // No change to project coverage :thumbsup:

Coverage data is based on head (10f35e7) compared to base (a4c6043). Patch coverage: 11.11% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #36 +/- ## ======================================= Coverage 61.35% 61.35% ======================================= Files 9 9 Lines 533 533 ======================================= Hits 327 327 Misses 206 206 ``` | [Impacted Files](https://codecov.io/gh/snek5000/snek5000-cbox/pull/36?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=snek5000) | Coverage Δ | | |---|---|---| | [tests/test\_slow\_RB.py](https://codecov.io/gh/snek5000/snek5000-cbox/pull/36/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=snek5000#diff-dGVzdHMvdGVzdF9zbG93X1JCLnB5) | `14.15% <0.00%> (ø)` | | | [tests/test\_slow\_sidewall.py](https://codecov.io/gh/snek5000/snek5000-cbox/pull/36/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=snek5000#diff-dGVzdHMvdGVzdF9zbG93X3NpZGV3YWxsLnB5) | `12.80% <0.00%> (ø)` | | | [tests/conftest.py](https://codecov.io/gh/snek5000/snek5000-cbox/pull/36/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=snek5000#diff-dGVzdHMvY29uZnRlc3QucHk=) | `90.00% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=snek5000). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=snek5000)

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[paugier]

Could you please rebase on main and edit the description of this PR to mention the related issue?