Trailing colon in PYTHONPATH

After installing lalsuite an sourcing the environment script etc/lalsuiterc, there can potentially be a trailing colon at the end of the PYTHONPATH. This occurs when PYTHONPATH is empty before sourcing, e.g.:

$ echo $PYTHONPATH

$ source /Users/wadelab/research/src/lscsoft/lalsuite/_inst-swig-mpi-eos-patch/etc/lalsuiterc
$ echo $PYTHONPATH
/Users/wadelab/research/src/lscsoft/lalsuite/_inst-swig-mpi-eos-patch/lib/python3.10/site-packages:

This was discussed on Mattermost, and I'm posting an issue here at @duncanmmacleod 's request so that folks don't forget to fix it.