refactor: simplifying directory setter property

[germa89]

Description

As the title.

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)

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[germa89]

@pyansys-ci-bot LGTM.

[pyansys-ci-bot]

✅ Approving this PR because germa89 said so in here 😬

[codecov]

Codecov Report

Attention: Patch coverage is 93.54839% with 2 lines in your changes missing coverage. Please review.

Project coverage is 82.40%. Comparing base (279cbba) to head (521473f).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3517      +/-   ##
==========================================
+ Coverage   82.36%   82.40%   +0.04%     
==========================================
  Files          57       58       +1     
  Lines       10004    10017      +13     
==========================================
+ Hits         8240     8255      +15     
+ Misses       1764     1762       -2