Settings Sync picks up theme change

[TylerLeonhardt-alt]

Testing #145616

Since you are automatically changing the theme color based on the OS, I don't think this theme change should be synced... otherwise, when I move to another machine where I don't use high contrast, my theme will be overwritten and the high contrast theme will be used and that will be jarring.

This is @TylerLeonhardt's alt account for linux testing

[TylerLeonhardt]

A symptom of this ... a few times for me this caused Settings Sync merge conflicts when I opened VS Code after switching on high contrast.

[aeschli]

Duplicate of #124572