Make the docs build successfully with mkdocstrings-python 2.0

[mitya57]

This fixes CI failure which can be seen here.

In mkdocstrings/python@5ebeda6 (1.14 release), two changes happened:

• import was renamed to inventories;
• passing extra options directly under options was deprecated, and they should be now passed in options.extra.

The old config kept working in 1.x releases, but since mkdocstrings/python@c10afdb (2.0 release), it no longer works.

I bumped mkdocstrings dependency to 0.28.3, because it in turn depends on mkdocstrings-python new enough to contain the first commit (see mkdocstrings/mkdocstrings@ba9003e).

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While working on this, I noticed that links to code are broken in the current release, because the tag name is 3.10.0 but _get_version() returns just 3.10. We should make this consistent, but that’s a separate issue.

[waylan]

Thanks for working through this. I just haven't had the time to look into it myself.