Some python tests fail on the ubuntu-clang CI

[egstern]

The tests test_nonlinear_maps.py and test_propagate.py in simulation/tests fail on the ubuntu-clang but on no other identified architectures.

In the case of test_nonlinear_maps.py, the lattice does not contain a BEAM statement. The madx parser parser looks for this statement to create a reference particle. A BEAM statement is not required for a lattice to be parsed. An error is thrown in the absence of this statement which is normally caught. however something goes wrong in the clang build when this is pybind11 wrapped and invoked from python so the catch doesn't work and a SEGV is generated. It works if this is not done through python.

In the case of test_propagator, an iterative structure is pybind11 wrapped. When this structure is iterated over in python, falling off the end of the iteration generates a SEGV in the case of ubuntu-clang. Again, this only happens in python.

Another issue will be opened to modify the tests to work around this problem. This issue is present so the problem is documented and remembered.