There's a closed pull request on the void-packages repository

python3: mark as EXTERNALLY-MANAGED
https://github.com/void-linux/void-packages/pull/43735

Description:
this prevents users from breaking xbps-installed python3 packages by using pip outside of a virtual environment. Error message adapted from gentoo's, debian's, and the example from PEP 668

see https://peps.python.org/pep-0668/ for more details

closes #43703

```
$ pip install --user foo
error: externally-managed-environment

× This environment is externally managed
╰─> 
    The system-wide Python installation in Void should be maintained
    using the system package manager, xbps.
    
    If the package in question is not packaged for Void, please
    consider installing it inside a virtual environment, e.g.:
    
    python3 -m venv /path/to/venv
    . /path/to/venv/bin/activate
    pip install mypackage
    
    To exit the virtual environment, run:
    
    deactivate
    
    The virtual environment is not deleted, and can be re-entered by
    re-sourcing the activate file.
    
    To automatically manage virtual environments, pipx (from python3-pipx)
    can be used.

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.
```

<!-- Uncomment relevant sections and delete options which are not applicable -->

#### Testing the changes
- I tested the changes in this PR: **YES**

#### TODOs

- [ ] write a news post notifying users of this change
- [x] (potentially) update [void-linux/void-containers](https://github.com/void-linux/void-containers) containers to not break due to this change

cc: @ahesford