Fix docs

[christofgehrig]

What does this PR do?

Fixes docs by updating the rtd theme. Also build docs in PRs (without deploy) to notice these bugs in the future.

Before submitting

• Did you make sure your PR does only one thing, instead of bundling different changes together?
• Did you list all the breaking changes introduced by this pull request?
• Did you test your PR locally with pytest command?
• Did you run pre-commit hooks with pre-commit run -a command?

[marcickler]

who let the docs (go) out?