Adwaita Demo doesn't respect Workbench color scheme

[sonnyp]

When Workbench is in dark mode, Adwaita Demo should open in dark mode as well.

See 10f597d

No idea if there is a way to set default color scheme to dark in a sandbox.

[sonnyp]

JCWasmx86 added plumbing to AdwStyleManager to allow GNOME Builder to launch apps with light/default/dark color scheme, as well as in high contrast. This has also been backported to Libhandy, and is available in 1.8.0 (which doesn’t have a blog post as it’s the only noteworthy change there).

https://blogs.gnome.org/alexm/2022/09/15/libadwaita-1-2/

so it's doable now \o/