[DPE-6042] Make tox commands resilient to white-space paths

[sinclert-canonical]

This PR fixes tox.ini commands when the repository is cloned on a white-space containing path.

How to reproduce:

$ mkdir -p "Projects/Canonical/Data Platform/MySQL"
$ cd "Projects/Canonical/Data Platform/MySQL"
$ git clone https://github.com/canonical/mysql-k8s-bundle
$ cd mysql-k8s-bundle
$ tox run -e format
> ...
> /Users/<USERNAME>/Projects/Canonical/Data:1:1: E902 No such file or directory (os error 2)
> Platform/MySQL/mysql-k8s-bundle/src:1:1: E902 No such file or directory (os error 2)
> Platform/MySQL/mysql-k8s-bundle/tests:1:1: E902 No such file or directory (os error 2)