feat: activate debug mode on testing using PYMAPDL_DEBUG_TESTING envvar

[germa89]

Description

Now using the envvar PYMAPDL_DEBUG_TESTING, we can produce more logs while testing.

Issue linked

Related to #3347 but for testing only

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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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.01%. Comparing base (b5e482a) to head (c1ce78a).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3594   +/-   ##
=======================================
  Coverage   87.01%   87.01%           
=======================================
  Files         187      187           
  Lines       14661    14661           
=======================================
  Hits        12757    12757           
  Misses       1904     1904           

[germa89]

@pyansys-ci-bot LGTM.

[pyansys-ci-bot]

✅ Approving this PR because germa89 said so in here 😬