Update tests to pass against upstream latest

[znicholls]

Description

Checklist

Please confirm that this pull request has done the following:

• Tests added
• Documentation added (where applicable)
• Changelog item added to changelog/

[znicholls]

Good to go: https://github.com/openscm/pandas-openscm/actions/runs/16317987357/job/46088416112

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.98%. Comparing base (580d612) to head (c3ff219).
⚠️ Report is 122 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #22   +/-   ##
=======================================
  Coverage   96.98%   96.98%           
=======================================
  Files          27       27           
  Lines        1358     1358           
  Branches      153      153           
=======================================
  Hits         1317     1317           
  Misses         23       23           
  Partials       18       18           

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