Fix generate_sensitivity_code=False for event sensitivity functions

[dweindl]

With generate_sensitivity_code=False, amici still generated some unnecessary event sensivity functions. This is fixed here.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.45%. Comparing base (9c82549) to head (f2cae53).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3044      +/-   ##
==========================================
- Coverage   78.10%   77.45%   -0.65%     
==========================================
  Files         311      311              
  Lines       20580    20580              
  Branches     1499     1499              
==========================================
- Hits        16073    15940     -133     
- Misses       4497     4630     +133     
  Partials       10       10              

Flag	Coverage Δ
cpp	70.71% <ø> (ø)
cpp_python	37.19% <ø> (ø)
petab	45.86% <ø> (ø)
petab_sciml	13.75% <ø> (ø)
python	69.37% <ø> (ø)
sbmlsuite-jax	?

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Files with missing lines	Coverage Δ
...on/sdist/amici/exporters/sundials/cxx_functions.py	97.14% <ø> (ø)

... and 5 files with indirect coverage changes

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