Noisy output in newest charmcraft

[dimaqq]

Bug Description

Building https://github.com/jnsgruk/hello-kubecon in CI, there's for example this:

 Installing dependencies
:: Running external command ['python3', '-m', 'venv', '/root/parts/charm/build/staging-venv']
:: Running external command ['/root/parts/charm/build/staging-venv/bin/pip', 'install', '--force-reinstall', 'pip@https://files.pythonhosted.org/packages/c0/d0/9641dc7b05877874c6418f8034ddefc809495e65caa14d38c7551cd114bb/pip-24.1.1.tar.gz']
::    :: WARNING: The directory '/root/.cache/pip' or its parent directory is not owned or is not writable by the current user. The cache has been disabled. Check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.

https://github.com/canonical/operator/actions/runs/12045070299/job/33583075577?pr=1461

To Reproduce

build a charm using charmcraft 3.2.2

Environment

CI, so amd64, charmcraft 3.2.2, targeting 20.04 I believe.

charmcraft.yaml

...

Relevant log output

...

[dimaqq]

To be fair, the command is run with --verbose.
But the .cache permission thing getting flagged is suggestive of something...