chore(deps): update actions/checkout action to v6

This PR contains the following updates: | Package | Type | Update | Change | |---|---|---|---| | [actions/checkout](https://redirect.github.com/actions/checkout) | action | major | `v4` → `v6` | --- ### Release Notes <details> <summary>actions/checkout (actions/checkout)</summary> ### [`v6`](https://redirect.github.com/actions/checkout/compare/v5...v6) [Compare Source](https://redirect.github.com/actions/checkout/compare/v5...v6) ### [`v5`](https://redirect.github.com/actions/checkout/compare/v4...v5) [Compare Source](https://redirect.github.com/actions/checkout/compare/v4...v5) </details> --- ### Configuration 📅 **Schedule**: Branch creation - "after 1am and before 5am" in timezone EST, 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. --- - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box --- This PR was generated by [Mend Renovate](https://mend.io/renovate/). View the [repository job log](https://developer.mend.io/github/techniq/svelte-ux). <!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiI0Mi43NC41IiwidXBkYXRlZEluVmVyIjoiNDIuNzQuNSIsInRhcmdldEJyYW5jaCI6Im1haW4iLCJsYWJlbHMiOlsiZGVwZW5kZW5jaWVzIl19-->