I picked the most recent versions that matched the newest stable GCC.
ParaStationMPI does not yet have GCC 11 modules and not sure about
stability of the GCC 11 module.

Better practice in order to separate the virtual environment cleanly
from the one it is started from.

This is simply clearer.

Could of course also use `./`, but then we may need to include `chmod
u+x` as well.