Update docutils constraint

[xylar]

Summary

Objectives:

• Get the docs to build with python 3.13
• Get docs building in CI in PRs, not just after merge

Select one: This pull request is...

• a bug fix: increment the patch version
• a small improvement: increment the minor version
• a new feature: increment the minor version
• an incompatible (non-backwards compatible) API change: increment the major version

Please fill out either the "Small Change" or "Big Change" section (the latter includes the numbered subsections), and delete the other.

Small Change

• To merge, I will use "Squash and merge". That is, this change should be a single commit.
• Logic: I have visually inspected the entire pull request myself.
• Pre-commit checks: All the pre-commits checks have passed.

fixes #387

[xylar]

I'm going to push a fix to #387 to this branch soon.

[xylar]

Unfortunately, these changes won't take effect until after we merge the PR, it looks like. That's because I renamed the job, I presume.

[xylar]

Ah, I take that back! It's running! Just took a sec.

[xylar]

This is working. Now getting sphinx 7.3.7 in build-docs instead of 5.3.0 in the the last main run of publish-docs.

[xylar]

@forsyth2, this fixes the issue as shown by passing build-docs test.

[forsyth2]

This is great, thanks @xylar!

[forsyth2]

Ok good, it passes the GitHub Actions: https://github.com/E3SM-Project/zstash/actions/runs/18234567528 & https://github.com/E3SM-Project/zstash/actions/runs/18234608651