Bump Avalonia.ReactiveUI and System.Text.Json

Bumps [Avalonia.ReactiveUI](https://github.com/AvaloniaUI/Avalonia) and [System.Text.Json](https://github.com/dotnet/runtime). These dependencies needed to be updated together.

Updates `Avalonia.ReactiveUI` from 11.1.4 to 11.2.1
- [Release notes](https://github.com/AvaloniaUI/Avalonia/releases)
- [Commits](AvaloniaUI/Avalonia@11.1.4...11.2.1)

Updates `System.Text.Json` from 8.0.5 to 8.0.3
- [Release notes](https://github.com/dotnet/runtime/releases)
- [Commits](dotnet/runtime@v8.0.5...v8.0.3)

---
updated-dependencies:
- dependency-name: Avalonia.ReactiveUI
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: System.Text.Json
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

src/MultiConverter/MultiConverter.csproj

@@ -11,7 +11,7 @@
     <PackageReference Include="Autofac" Version="8.1.1" />
     <!--Condition below is needed to remove Avalonia.Diagnostics package from build output in Release configuration.-->
     <PackageReference Condition="'$(Configuration)' == 'Debug'" Include="Avalonia.Diagnostics" Version="11.1.4" />
-    <PackageReference Include="Avalonia.ReactiveUI" Version="11.1.4" />
+    <PackageReference Include="Avalonia.ReactiveUI" Version="11.2.1" />
     <PackageReference Include="Avalonia.Xaml.Behaviors" Version="11.1.0.4" />
     <PackageReference Include="FluentAvaloniaUI" Version="2.1.0" />
     <PackageReference Include="Microsoft.Extensions.Configuration" Version="8.0.0" />