C++ coverage is not working like in Travis

Coverage for pure-python packages is already covered with the latest updates on the build instructions and environments.

One issue remains - how to both compile code with coverage support (not currently working for this package).

See, for example, https://gitlab.idiap.ch/bob/bob.blitz/builds/4206

To be checked, if this is caused by missing versions of profiling versions of libstdc++ and if that can be installed with Conda.