Fix sympy symbol name clashes during PEtab import

[dweindl]

Closes #2055

[codecov]

Codecov Report

Merging #2069 (f497360) into develop (f8929b9) will not change coverage.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #2069   +/-   ##
========================================
  Coverage    54.90%   54.90%           
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  Files           30       30           
  Lines         4617     4617           
========================================
  Hits          2535     2535           
  Misses        2082     2082           

Flag	Coverage Δ
petab	54.90% <100.00%> (ø)

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Impacted Files	Coverage Δ
python/sdist/amici/petab_objective.py	93.77% <ø> (ø)
python/sdist/amici/petab_import.py	69.41% <100.00%> (ø)

[FFroehlich]

intentional that this doesn't cover all call to sympy.sympify?

[dweindl]

intentional that this doesn't cover all call to sympy.sympify?

Yes. The ones in the SBML and PySB importers should be fine. There, we already gather all model symbols beforehand and pass them as locals.