update avalonia with debian 9 compatibility fixes.
MODIFY
Directory.Build.targets
Directory.Build.targets
<Project>
<PropertyGroup>
- <AvaloniaVersion>0.7.1-build1281-beta</AvaloniaVersion>
+ <AvaloniaVersion>0.7.1-build1286-beta</AvaloniaVersion>
<AvaloniaBehaviorsVersion>0.7.0</AvaloniaBehaviorsVersion>
</PropertyGroup>

MODIFY
WalletWasabi.Dependencies/AvalonStudio.Shell
WalletWasabi.Dependencies/AvalonStudio.Shell
-Subproject commit 16a564e1891e43d8b688b483f4f2830b97ddf38e
+Subproject commit 56cae3909935c83973bcb7e3810cf3b635110c3d

update avalonia with debian 9 compatibility fixes.