Fix Readthedocs build

[HenrZu]

Changes and Information

Please briefly list the changes (main added features, changed items, or corrected bugs) made:

• New version of pip/setuptools leads to failed build (fails in setup.py from generation pkg)
• Use installed packages from requirements-build (just for building the doc) via --no-build-isolation
• Will soon be much easier, when switching to toml instalation Switch from setup.py to pyproject.toml #1111

If need be, add additional information and what the reviewer should look out for in particular:

Merge Request - Guideline Checklist

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Checks by code author

• Every addressed issue is linked (use the "Closes #ISSUE" keyword below)
• New code adheres to coding guidelines
• No large data files have been added (files should in sum not exceed 100 KB, avoid PDFs, Word docs, etc.)
• Tests are added for new functionality and a local test run was successful (with and without OpenMP)
• Appropriate documentation within the code (Doxygen) for new functionality has been added in the code
• Appropriate external documentation (ReadTheDocs) for new functionality has been added to the online documentation
• Proper attention to licenses, especially no new third-party software with conflicting license has been added
• (For ABM development) Checked benchmark results and ran and posted a local test above from before and after development to ensure performance is monitored.

Checks by code reviewer(s)

• Corresponding issue(s) is/are linked and addressed
• Code is clean of development artifacts (no deactivated or commented code lines, no debugging printouts, etc.)
• Appropriate unit tests have been added, CI passes, code coverage and performance is acceptable (did not decrease)
• No large data files added in the whole history of commits(files should in sum not exceed 100 KB, avoid PDFs, Word docs, etc.)
• On merge, add 2-5 lines with the changes (main added features, changed items, or corrected bugs) to the merge-commit-message. This can be taken from the briefly-list-the-changes above (best case) or the separate commit messages (worst case).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.24%. Comparing base (cff9ccb) to head (30e87a5).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1403      +/-   ##
==========================================
- Coverage   97.27%   97.24%   -0.03%     
==========================================
  Files         176      176              
  Lines       15517    15517              
==========================================
- Hits        15094    15090       -4     
- Misses        423      427       +4     

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[kilianvolmer]

Thanks for repairing that quickly!