Remove deprecated noise parameter for GPs

[williambdean]

Description

Follow up to PR #6145 three years ago

Related Issue

• Closes #
• Related to #

Checklist

• Checked that the pre-commit linting/style checks pass
• Included tests that prove the fix is effective or that the new feature works
• Added necessary documentation (docstrings and/or example notebooks)
• If you are a pro: each commit corresponds to a relevant logical change

Type of change

• New feature / enhancement
• Bug fix
• Documentation
• Maintenance
• Other (please specify):

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📚 Documentation preview 📚: https://pymc--7886.org.readthedocs.build/en/7886/

[williambdean]

need to change the tests still and remove None default value for sigma

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.94%. Comparing base (127ac30) to head (6bb279b).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7886      +/-   ##
==========================================
- Coverage   92.95%   92.94%   -0.01%     
==========================================
  Files         116      116              
  Lines       18863    18851      -12     
==========================================
- Hits        17534    17522      -12     
  Misses       1329     1329              

Files with missing lines	Coverage Δ
pymc/gp/gp.py	94.71% <100.00%> (-0.16%)	⬇️

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[ricardoV94]

Thanks @williambdean