feat: running MPI fix only if on windows

[germa89]

Description

As the title. To simplify stuff.

Issue linked

NA

Checklist

• I have visited and read Develop PyMAPDL.
• I have tested my changes locally
• I have added necessary documentation or updated existing documentation.
• I have followed the PyMAPDL coding style guidelines.
• I have added appropriate unit tests that also ensure the minimal coverage criteria.
• I have reviewed my changes before submitting this pull request.
• I have linked the issue or issues that are solved to the PR if any.
• I have assigned this PR to myself.
• I have marked this PR as draft if it is not ready to be reviewed yet.
• I have made sure that the title of my PR follows Commit naming conventions (e.g. feat: adding new MAPDL command)

[ansys-reviewer-bot]

Thanks for opening a Pull Request. If you want to perform a review write a comment saying:

@ansys-reviewer-bot review

[germa89]

@pyansys-ci-bot LGTM.

[pyansys-ci-bot]

✅ Approving this PR because germa89 said so in here 😬

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.93%. Comparing base (853daba) to head (3e16ef1).
Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3575      +/-   ##
==========================================
- Coverage   86.93%   86.93%   -0.01%     
==========================================
  Files         187      187              
  Lines       14616    14622       +6     
==========================================
+ Hits        12707    12711       +4     
- Misses       1909     1911       +2