Prepare release: 1.4.0

[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 workflow, triggered by @MetRonnie

Tests:

• Tests last run on master:
• ✔️ Build check passed - see the workflow run (number 15) for more info

Checklist:

• [x] Milestone complete? 0 other open issues/PRs on milestone 1.4.0 at time of PR creation
• [x] No changelog

Next steps:

• @MetRonnie 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)

[MetRonnie]

Going for a minor release instead of patch because it includes update from Cylc 7 -> 8 graph syntax

[oliver-sanders]

All good, leaving you to merge.

[github-actions[bot]]

✔️ success

Next steps for @MetRonnie:

• 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: 13