chore(deps): update actions/checkout action to v4

[renovate]

This PR contains the following updates:

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

---

Release Notes

actions/checkout (actions/checkout)

v4

Compare Source

• Check out other refs/* by commit if provided, fall back to ref by @​orhantoy in https://github.com/actions/checkout/pull/1924

---

Configuration

📅 Schedule: Branch creation - "every 2 weeks on Monday before 7am" in timezone Europe/Berlin, 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]

✅ Deploy Preview for weihnachtsmarktkarte ready!

Name	Link
🔨 Latest commit	ad0299a
🔍 Latest deploy log	https://app.netlify.com/sites/weihnachtsmarktkarte/deploys/64fe3d4bce2ed100081c5891
😎 Deploy Preview	https://deploy-preview-75--weihnachtsmarktkarte.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

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