Prepare release: 2.3.1

[github-actions[bot]]

⚡ Merging this PR will automatically create a GitHub Release & publish the package ⚡

This PR was created by the Release stage 1 - create release PR (Rose 2+ only) workflow, triggered by @oliver-sanders

Tests:

• Tests last run on 2.3.x:
• ✔️ Build check passed - see the workflow run (number 20) for more info

Checklist:

• [x] Milestone complete? 0 other open issues/PRs on milestone 2.3.1 at time of PR creation

Next steps:

• @oliver-sanders should request 1 or 2 reviews
• If any further changes are needed, push to this PR branch
• After merging, the bot will comment below with a link to the release (if not, look at the PR checks tab)

[!IMPORTANT] Do not use [skip ci] in commit messages pushed to this PR, as it will prevent the 2nd stage release workflow from running.

[oliver-sanders]

Bugfix release to get the template variables -> template_variables fix out.

[oliver-sanders]

• Mac OS build currently failing (plz ignore).
• Docs build currently failing (on linkcheck build, low consequence).

[github-actions[bot]]

✔️ success

Next steps for @oliver-sanders:

• view/edit the GitHub release description as appropriate
• ✔️ Milestone automatically closed

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Comment created by workflow: Release stage 2 - auto publish, run: 36