Add windows stub for restart_webhelper

[suchmememanyskill]

Please tick as appropriate:

• [X] I have tested this code on a steam deck or on a PC
  • Windows specific
• [X] My changes generate no new errors/warnings
• [X] This is a bugfix/hotfix
• [ ] This is a new feature

If you're wanting to update a translation or add a new one, please use the weblate page: https://weblate.werwolv.net/projects/decky/

Description

This fixes issue: Windows client crashing on boot due to a missing import