x11/walker: Update to 2.5.4

Changelog:

• https://github.com/abenz1267/walker/releases/tag/v2.5.1
• https://github.com/abenz1267/walker/releases/tag/v2.5.2
• https://github.com/abenz1267/walker/releases/tag/v2.5.3
• https://github.com/abenz1267/walker/releases/tag/v2.5.4

Reported by: GitHub (watch releases)