Don't build swig

[dweindl]

Meanwhile, we use swig from PyPI. There is currently no need to build swig ourselves. That version was anyways shadowed by PyPI-swig.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.02%. Comparing base (3ada40c) to head (f626049).
⚠️ Report is 93 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3003      +/-   ##
==========================================
- Coverage   76.70%   76.02%   -0.68%     
==========================================
  Files         309      309              
  Lines       19891    19891              
  Branches     1498     1498              
==========================================
- Hits        15258    15123     -135     
- Misses       4620     4755     +135     
  Partials       13       13              

Flag	Coverage Δ
cpp	72.53% <ø> (ø)
cpp_python	37.87% <ø> (ø)
petab	38.58% <ø> (ø)
petab_sciml	14.14% <ø> (ø)
python	69.35% <ø> (ø)
sbmlsuite-jax	?

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see 6 files with indirect coverage changes

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