Bump ReactiveUI.Testing from 19.4.1 to 19.5.1

Bumps [ReactiveUI.Testing](https://github.com/reactiveui/reactiveui) from 19.4.1 to 19.5.1.
- [Release notes](https://github.com/reactiveui/reactiveui/releases)
- [Commits](reactiveui/ReactiveUI@19.4.1...19.5.1)

---
updated-dependencies:
- dependency-name: ReactiveUI.Testing
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

tests/ImageSort.UnitTests/ImageSort.UnitTests.csproj

@@ -12,7 +12,7 @@
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.7.2" />
     <PackageReference Include="Moq" Version="4.20.69" />
     <PackageReference Include="ReactiveUI" Version="19.4.1" />
-    <PackageReference Include="ReactiveUI.Testing" Version="19.4.1" />
+    <PackageReference Include="ReactiveUI.Testing" Version="19.5.1" />
     <PackageReference Include="xunit" Version="2.5.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.1">
       <PrivateAssets>all</PrivateAssets>