x11/walker: Update to 2.7.1

Changelog:

• https://github.com/abenz1267/walker/releases/tag/v2.6.3
• https://github.com/abenz1267/walker/releases/tag/v2.6.4
• https://github.com/abenz1267/walker/releases/tag/v2.7.0
• https://github.com/abenz1267/walker/releases/tag/v2.7.1

Reported by: GitHub (watch releases)