CI: Remove redundant tests.

[dweindl]

Remove test_observable_events which meanwhile is redundant with test_pregenerated_models.test_pregenerated_model_py.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.88%. Comparing base (7029db0) to head (c6bf75d).
⚠️ Report is 54 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2919      +/-   ##
==========================================
- Coverage   79.64%   78.88%   -0.76%     
==========================================
  Files         358      358              
  Lines       23044    23044              
  Branches     1581     1581              
==========================================
- Hits        18353    18179     -174     
- Misses       4680     4854     +174     
  Partials       11       11              

Flag	Coverage Δ
cpp	74.81% <ø> (-0.20%)	⬇️
cpp_python	33.18% <ø> (ø)
petab	38.96% <ø> (ø)
python	73.67% <ø> (-0.20%)	⬇️
sbmlsuite-jax	?

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see 10 files with indirect coverage changes

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