Update actions/upload-artifact action to v4

[renovate[bot]]

This PR contains the following updates:

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

---

Release Notes

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

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

---

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.

---

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

---

This PR was generated by Mend Renovate. View the repository job log.

[netlify[bot]]

✅ Deploy Preview for leipziger-weihnachtsmaerkte ready!

Name	Link
🔨 Latest commit	76bdfc831ac0fa0a8dcb96671524a410291aecde
🔍 Latest deploy log	https://app.netlify.com/sites/leipziger-weihnachtsmaerkte/deploys/67395bfa9f6c380008c6b55c
😎 Deploy Preview	https://deploy-preview-41--leipziger-weihnachtsmaerkte.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.
Lighthouse	1 paths audited Performance: 31 Accessibility: 76 Best Practices: 92 SEO: 100 PWA: 70 View the detailed breakdown and full score reports

---

To edit notification comments on pull requests, go to your Netlify site configuration.