petab-import: fix fixed parameter selection with pandas>=3

[dweindl]

Fixes a pandas>=3.0 compatibility issue in the PEtab importer which resulted in incorrect selection of fixed parameters.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.76%. Comparing base (33affbf) to head (86bd6bd).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3161      +/-   ##
==========================================
- Coverage   77.36%   76.76%   -0.61%     
==========================================
  Files         317      317              
  Lines       20631    20631              
  Branches     1483     1483              
==========================================
- Hits        15961    15837     -124     
- Misses       4662     4786     +124     
  Partials        8        8              

Flag	Coverage Δ
cpp	70.49% <100.00%> (+0.03%)	⬆️
cpp_python	37.15% <50.00%> (ø)
petab	47.17% <100.00%> (ø)
python	68.95% <100.00%> (+0.03%)	⬆️
sbmlsuite-jax	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
.../sdist/amici/importers/petab/v1/_import_helpers.py	85.71% <ø> (ø)
...n/sdist/amici/sim/sundials/petab/v1/_conditions.py	98.33% <100.00%> (ø)

... and 5 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.