build(deps): update ReactiveUI requirement from 12.* to 13.* (#130)

Updates the requirements on [ReactiveUI](https://github.com/reactiveui/reactiveui) to permit the latest version.
- [Release notes](https://github.com/reactiveui/reactiveui/releases)
- [Commits](reactiveui/ReactiveUI@12.1.1...13.0.1)

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

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

src/Fusillade.Tests/Fusillade.Tests.csproj

@@ -14,7 +14,7 @@
   <ItemGroup>
     <PackageReference Include="akavache" Version="7.*" />
     <PackageReference Include="DynamicData" Version="7.*" />
-    <PackageReference Include="ReactiveUI" Version="12.*" />
+    <PackageReference Include="ReactiveUI" Version="13.*" />
     <PackageReference Include="ReactiveUI.Testing" Version="12.*" />
   </ItemGroup>
 </Project>