[docs] Class diagrams are scaled incorrectly

[pavel-kirienko]

This is not reproducible on my local machine but is visible only on ReadTheDocs:

The difference is in the scale transform used in the generated SVG file. This is visible on the ReadTheDocs website:

This is on my local machine:

The obvious thing is that the graphviz (dot) version is different: the latest version in Ubuntu 22.04 is v2.43, which is reported in the generated SVG file, while on my machine (Manjaro) I have v9.0.

We should either set the scale explicitly or make ReadTheDocs use an up-to-date version of Graphviz. One way to do the latter is to grab the DEB package from the release page at https://gitlab.com/graphviz/graphviz/-/releases and install it using a pre-build job as documented in the readthedocs docs.