Bump CommunityToolkit.Mvvm from 8.3.2 to 8.4.0

Bumps [CommunityToolkit.Mvvm](https://github.com/CommunityToolkit/dotnet) from 8.3.2 to 8.4.0.
- [Release notes](https://github.com/CommunityToolkit/dotnet/releases)
- [Commits](CommunityToolkit/dotnet@v8.3.2...v8.4.0)

---
updated-dependencies:
- dependency-name: CommunityToolkit.Mvvm
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Directory.Packages.props

@@ -6,7 +6,7 @@
   -->
   <ItemGroup>
     <!--Emerald.App-->
-    <PackageVersion Include="CommunityToolkit.Mvvm" Version="8.3.2" />
+    <PackageVersion Include="CommunityToolkit.Mvvm" Version="8.4.0" />
     <PackageVersion Include="CommunityToolkit.WinUI.Controls.SettingsControls" Version="8.1.240916" />
     <PackageVersion Include="CommunityToolkit.WinUI.Converters" Version="8.1.240916" />
     <PackageVersion Include="CommunityToolkit.WinUI.Helpers" Version="8.1.240916" />