fix: path to tutor executable for settheme command

Description

Fixes the tutor invocation when calling settheme to use the virtual environment's executable

Testing instructions

Steps to test the changes:

Original pipeline: https://gitlab.com/opencraft/devstacks/keith/grove-do/-/jobs/3824606887 There will be text like

⚠️  Failed to enable plugin 'forum': plugin 'forum' is not installed.
⚠️  Failed to enable plugin 'grove': plugin 'grove' is not installed.

Fixed pipeline: https://gitlab.com/opencraft/devstacks/keith/grove-do/-/jobs/3828369385

Checklist

If any of the items below is not applicable, do not remove them, but put a check in it.

• All providers include the new feature/change
• All affected providers can provision new clusters
• Unit tests are added/updated
• Documentation is added/updated
• The TOOLS_CONTAINER_IMAGE_VERSION in ci_vars.yml is updated
• The grove-template repository is updated