docs/conf.py has a hardcoded (and wrong) version string

[grahamgower]

This should be read from the version in stdpopsim/_version.py. E.g.
https://github.com/tskit-dev/tskit/blob/main/docs/conf.py#L52-L53

[jeromekelleher]

Since stdpopsim uses setuptools_scm, it's better to use their infrastructure for determining the version. See how msprime does it here

(FYI tskit doesn't use setuptools_scm because it's a multi-package repo and this confused setuptools_scm)

[andrewkern]

reopening this because even though #1674 includes the version, the github action we are using (checkout@v4) doesn't by default clone the repo with the tags (which is where setuptools_scm looks for version/release info). instead it does a shallow clone of the repo.

the fix i believe is to give the action here an option that looks like

with:
    fetch-depth: 0 # will get all tags