labwc: change wallpaper to desert sunset

[humaidq-tii]

Description of changes

• Change wallpaper

Checklist for things done

• [x] Summary of the proposed changes in the PR description
• [x] More detailed description in the commit message(s)
• [x] Commits are squashed into relevant entities - avoid a lot of minimal dev time commits in the PR
• [x] Contribution guidelines followed
• [ ] Ghaf documentation updated with the commit - https://tiiuae.github.io/ghaf/
• [ ] PR linked to architecture documentation and requirement(s) (ticket id)
• [ ] Test procedure described (or includes tests). Select one or more:
  • [ ] Tested on Lenovo X1 x86_64
  • [ ] Tested on Jetson Orin NX or AGX aarch64
  • [ ] Tested on Polarfire riscv64
• [ ] Author has run make-checks and it passes
• [ ] All automatic Github Action checks pass - see actions
• [ ] Author has added reviewers and removed PR draft status
• [ ] Change requires full re-installation: no
• [x] Change can be updated with nixos-rebuild ... switch: yes but gui-vm will restart

Instructions for Testing

• [x] List all targets that this applies to: x1, orin
• [ ] Is this a new feature
  • [ ] List the test steps to verify:
• [ ] If it is an improvement how does it impact existing functionality?

[humaidq-tii]

Closed as this change will be carried by @kajusnau 's PR