Update purcell/setup-emacs action to v4

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
purcell/setup-emacs	action	major	v3.0 -> v4.0

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Release Notes

purcell/setup-emacs

### [`v4.0`](https://togithub.com/purcell/setup-emacs/compare/v3.0...v4.0) [Compare Source](https://togithub.com/purcell/setup-emacs/compare/v3.0...v4.0)

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Configuration

📅 Schedule: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 Ignore: Close this PR and you won't be reminded about this update again.

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• [ ] If you want to rebase/retry this PR, check this box

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