Hot fix test PyPI install

[znicholls]

Description

Running happily now: https://github.com/openscm/example-fgen-basic/actions/runs/17265386538/job/48996152162

Checklist

Please confirm that this pull request has done the following:

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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (e3d62f8) to head (147e604).
⚠️ Report is 63 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #26   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            3         3           
  Lines           18        18           
=========================================
  Hits            18        18           

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