Update version and changelog for the release of 2.13.0rc4

[jlenh]

Description

Cherry-picked some additional commits to include in ESMValCore before the new recipe testing round:

• Use pip install --no-deps to avoid overwiting packages from the conda environment #2829
• replace nbsphinx with myst-nb and remove pin on ipython #2838
• Repair gha tests after pip install with no deps and add working reference to ipynb Jupyter notebooks in docs #2844

Link to documentation: https://esmvaltool--2849.org.readthedocs.build/projects/ESMValCore/en/2849/changelog.html#v2-13-0

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.46%. Comparing base (6a4941e) to head (9b1a8bd).
⚠️ Report is 62 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2849   +/-   ##
=======================================
  Coverage   95.46%   95.46%           
=======================================
  Files         260      260           
  Lines       15526    15526           
=======================================
  Hits        14822    14822           
  Misses        704      704           

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