Ensure Steam Deck pulls Linux build

[jaredkrinke]

Make sure it doesn't attempt to use the Windows/Proton version, because that won't work (lack of WebView2).

[jaredkrinke]

Everything worked fine on Linux Mint Cinnamon. Issues reported for SteamDeck:

• Defaulted to Windows build (which doesn't work, due to WebView2)
• Buttons didn't work unless fullscreened
• Audio didn't work

Those second two issues are eerily similar to the problems I encountered when trying to use a Windows Electron build via Proton. But the player reported they were using Steam Linux Runtime 1.0 (scout), so that shouldn't be related...