docs: use :signatures: none

[pjonsson]

Reason for this pull request

The :nosignatures: clause is
supserseded by :signatures: none
according to the documentation,
so use that.

Proposed changes

• Closes #xxxx

• Tests added / passed

• Pull Request Title will make sense in ODC Release Notes

---

📚 Documentation preview 📚: https://opendatacube--2236.org.readthedocs.build/en/2236/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.10%. Comparing base (be760cb) to head (898b356).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #2236   +/-   ##
========================================
  Coverage    86.10%   86.10%           
========================================
  Files          155      155           
  Lines        16802    16802           
========================================
  Hits         14467    14467           
  Misses        2335     2335           

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[pjonsson]

This requires Sphinx 8.2, which we apparently can't update to because that requires Python 3.11.