Fix for Python error: This environment is externally managed

[havardthom]

Original thread: tteck/Proxmox#3300

TLDR: Execute rm -rf /usr/lib/python3.*/EXTERNALLY-MANAGED in the LXC console.

Users that manually updates an LXC to Debian 12.6 will reintroduce the /usr/lib/python3.*/EXTERNALLY-MANAGED file, causing the error below when installing python packages with pip. Remove this file by executing rm -rf /usr/lib/python3.*/EXTERNALLY-MANAGED in the LXC console.

If you install new scripts or update LXCs using the LXC updater script you will not have this problem.

× This environment is externally managed
╰─> To install Python packages system-wide, try apt install
    python3-xyz, where xyz is the package you are trying to
    install.
    
    If you wish to install a non-Debian-packaged Python package,
    create a virtual environment using python3 -m venv path/to/venv.
    Then use path/to/venv/bin/python and path/to/venv/bin/pip. Make
    sure you have python3-full installed.
    
    If you wish to install a non-Debian packaged Python application,
    it may be easiest to use pipx install xyz, which will manage a
    virtual environment for you. Make sure you have pipx installed.
    
    See /usr/share/doc/python3.11/README.venv for more information.

note: If you believe this is a mistake, please contact your Python installation or OS distribution provider. You can override this, at the risk of breaking your Python installation or OS, by passing --break-system-packages.
hint: See PEP 668 for the detailed specification.