ci: remove unused stale issue and release configuration files

[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)

[Copilot]

Pull Request Overview

This PR removes unused CI configuration files for issue management and release automation. The purpose is to clean up the repository by removing stale configuration files that are no longer needed.

• Removes the stale issue bot configuration file
• Removes the GitHub release changelog configuration file

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
.github/stale.yml	Completely removes the stale issue automation configuration
.github/release.yml	Completely removes the GitHub release changelog configuration

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_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.28%. Comparing base (1268ded) to head (888d506).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4195      +/-   ##
==========================================
- Coverage   91.39%   91.28%   -0.12%     
==========================================
  Files         193      193              
  Lines       15731    15731              
==========================================
- Hits        14378    14360      -18     
- Misses       1353     1371      +18     

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[germa89]

@pyansys-ci-bot LGTM

[pyansys-ci-bot]

✅ Approving this PR because germa89 said so in here 😬