Set version to 1.8.1

[mortenpi]

To get #2624 out.

---

Pre-release

• Change the version number in Project.toml
  • If the release is breaking, increment MAJOR
  • If the release adds a new user-visible feature, increment MINOR
  • Otherwise (bug-fixes, documentation improvements), increment PATCH
• Update CHANGELOG.md, following the existing style (in particular, make sure that the change log for this version has the correct version number and date).
• Run make changelog, to make sure that all the issue references in CHANGELOG.md are up to date.
• Check that the commit messages in this PR do not contain [ci skip]
• Run regression-tests workflow using a workflow_dispatch trigger to check for any changes that broke extensions: https://github.com/JuliaDocs/Documenter.jl/actions/runs/13258266800

The release

• After merging the pull request, tag the release. There are two options for this:

  1. Comment [at]JuliaRegistrator register on the GitHub commit.
  2. Use JuliaHub's package registration feature to trigger the registration.

  Either of those should automatically publish a new version to the Julia registry.

• Once registered, the TagBot.yml workflow should create a tag, and rebuild the documentation for this tag.

• These steps can take quite a bit of time (1 hour or more), so don't be surprised if the new documentation takes a while to appear.