[CI] fails occasionally (mo_objective_function)

@kaluza and me (@muellese) noticed, that the gitlab CI fails occasionally, because it can't compile mhm since it is missing mo_objective_function.mod.

This happens for all compilers (gcc83, intel20, nag62 already reported)

This can be fixed at occurrence with a retry or deleting the build folder on eve (/public/mhm_runner/....).

I am at my wit's end. At least for now