Add flag to allow global installs e.g. for CI

[zanieb]

We require install into a virtual environment, but in ephemeral builds like CI or containers this may not be desired.

[yabirgb]

I was facing the same issue. Maybe provide a --no-envor --global variable so the user can't do it by accident

[justinh-rahb]

Ya, this has been a blocker to using this to speed up some slow container builds unfortunately.

[henryiii]

Workaround credit to @matthewfeickert:

    - name: Set the VIRTUAL_ENV variable for uv to work
      run: |
        echo "VIRTUAL_ENV=${Python_ROOT_DIR}" >> $GITHUB_ENV

[matthewfeickert]

I actually took that from #1386 (comment) and #1386 (comment). The important bit here is that it needs to be done in a seperate step before you want to use it, so you can't modify the $GITHUB_ENV in the same run command as you want to use it.

[zanieb]

This is a duplicate of #1374; oops. I'll keep both for now since they're distinct titles.

[hauntsaninja]

(Naming the flag --system would mirror venv's --system-site-packages)

[yabirgb]

I got this error pointing the env to the python location as @henryiii posted. Did anyone face the same issue? In the docker container it worked fine

rotki/rotki#7499

[charliermarsh]

I am a fan of a system flag though @zanieb has done a lot more work on the Python discovery stuff.