fix(ci): avoid python3.10 reference; don't install bokeh, pygithub

[wdconinc]

Briefly, what does this PR introduce?

We are using python3.11 now, so the pip install would install to ~/.local/lib/python3.11/site-packages if it did anything, and the hardcoded PYTHONPATH prepend would then fail to find the module. That this continued to work demonstrates that we don't need to install anything locally, and can get rid of the PYTHONPATH modifications too.

This PR removes the PYTHONPATH additions and the custom pip install. If an update to the bokeh and pygithub packages are needed, then this is better handled by updating what is in the container, now that we have reached a more stable capybara stage of development.

What kind of change does this PR introduce?

• Bug fix (issue: hardcoded reference to python3.10)
• New feature (issue #__)
• Documentation update
• Other: __

Please check if this PR fulfills the following:

• Tests for the changes have been added
• Documentation has been added / updated
• Changes have been communicated to collaborators

Does this PR introduce breaking changes? What changes might users need to make to their code?

No.

Does this PR change default behavior?

No.

[veprbl]

No objections, of course