Remove custom environment variable PYTHONPATH

Locations:

• https://gitlab.b-data.ch/jupyterlab/qgis/docker-stack/-/blob/01839fd15a3aca6d9de69c2c6f99a3631171731a/base/conf/user/var/backups/skel/.local/share/QGIS/QGIS3/profiles/default/QGIS/QGIS3.ini
  • https://gitlab.b-data.ch/jupyterlab/qgis/docker-stack/-/blob/01839fd15a3aca6d9de69c2c6f99a3631171731a/NOTES.md?plain=1#L139-142
• https://gitlab.b-data.ch/jupyterlab/r/docker-stack/-/blob/d9c3f9aa5197ed79081c3af71f66bc46a21af3b5/qgisprocess/conf/user/var/backups/skel/.local/share/QGIS/QGIS3/profiles/default/QGIS/QGIS3.ini
  • https://gitlab.b-data.ch/jupyterlab/r/docker-stack/-/blob/d9c3f9aa5197ed79081c3af71f66bc46a21af3b5/NOTES.md?plain=1#L176-179
• https://gitlab.b-data.ch/r/docker-stack/-/blob/21a6446ccadf10887f02251372d80606c5d9d18f/qgisprocess/latest.Dockerfile#L201-207

For versions 3.46.4 (new LTR) and 3.48.0 (new stable).