Update GitHub Artifact Actions to v4 (major)

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
actions/download-artifact	action	major	v3 -> v4
actions/upload-artifact	action	major	v3 -> v4

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Release Notes

actions/download-artifact (actions/download-artifact)

### [`v4`](https://togithub.com/actions/download-artifact/compare/v3...v4) [Compare Source](https://togithub.com/actions/download-artifact/compare/v3...v4)

actions/upload-artifact (actions/upload-artifact)

### [`v4`](https://togithub.com/actions/upload-artifact/compare/v3...v4) [Compare Source](https://togithub.com/actions/upload-artifact/compare/v3...v4)

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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: Never, or you tick the rebase/retry checkbox.

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

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

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[valtterikantanen]

Do not merge this, v4 doesn't work without changes to GHA workflow files