Add full installation of package to compile docs

[ninamiolane]

The workflow to deploy docs actually needs the full TBX package install.

This PR adds it.

Otherwise, torch-sparse missing to render API docs

Checklist

• My pull request has a clear and explanatory title.
• My pull request passes the Linting test.
• I added appropriate unit tests and I made sure the code passes all unit tests. (refer to comment below)
• My PR follows PEP8 guidelines. (refer to comment below)
• My code is properly documented, using numpy docs conventions, and I made sure the documentation renders properly.
• I linked to issues and PRs that are relevant to this PR.

Description

Issue

Additional context