test: skip database tests based on TEST_DB environment variable

[germa89]

Description

Skip database tests if TEST_DB env var does not exist or it is different than "true".

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)

[germa89]

@pyansys-ci-bot LGTM.

[Copilot]

Pull Request Overview

This PR implements conditional skipping of database tests based on the TEST_DB environment variable to allow more flexible test execution control.

• Adds TEST_DB environment variable check to skip database tests when not needed
• Implements skip logic in both test fixture and individual test function
• Provides consistent test execution behavior based on environment configuration

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[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 91.32%. Comparing base (651042d) to head (ab155ba).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4250      +/-   ##
==========================================
+ Coverage   91.20%   91.32%   +0.12%     
==========================================
  Files         193      193              
  Lines       15719    15719              
==========================================
+ Hits        14336    14356      +20     
+ Misses       1383     1363      -20     

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