This MR fixes the ggF_HH process, after the subsequent fix of the powheg installation in
The changes in the process interface would create symbolic links to files which are in the process directory, and which need to be present locally. Also, since this process uses a python code which uses scipy, we have to expand
PYTHONPATH so that this python module is made available (this is a priory a temporary fix until we find a way to include scipy in AthGeneration).
We a priori do not need to sweep this MR to master because the python code (and its C interface) used by this process is written in python2 explicitely (so we would have to discuss this with Powheg authors).
Alternatively the sweep to master could still be made in case we want to be consistent - but this process won't work anyway in 22.6 at the moment.