update avalonia with merged mem leak fixes.
MODIFY
Directory.Build.targets
Directory.Build.targets
<Project>
<PropertyGroup>
- <AvaloniaVersion>0.7.1-cibuild0001553-beta</AvaloniaVersion>
+ <AvaloniaVersion>0.7.1-cibuild0001581-beta</AvaloniaVersion>
<AvaloniaBehaviorsVersion>0.7.0</AvaloniaBehaviorsVersion>
</PropertyGroup>

MODIFY
WalletWasabi.Dependencies/AvalonStudio.Shell
WalletWasabi.Dependencies/AvalonStudio.Shell
-Subproject commit b480f0ce896111dc1ca94dde4a05ea6b914b5f5f
+Subproject commit 8163735bc84048eccc15f0cf30d71823f34ae495

MODIFY
nuget.config
nuget.config
<packageSources>
<add key="nuget.org" value="https://www.nuget.org/api/v2/" />
<add key="AvaloniCI" value="https://www.myget.org/F/avalonia-ci/api/v2" />
- <add key="AvaloniPRs" value="https://www.myget.org/F/avalonia-prs/api/v2" />
<add key="XamlBehaviors" value="https://www.myget.org/F/xamlbehaviors-nightly/api/v2" />
<add key="DockNightly" value="https://www.myget.org/F/dock-nightly/api/v2" />
</packageSources>

update avalonia with merged mem leak fixes.