build(deps): Bump ReactiveUI.Testing from 18.4.26 to 19.2.1

Bumps [ReactiveUI.Testing](https://github.com/reactiveui/reactiveui) from 18.4.26 to 19.2.1.
- [Release notes](https://github.com/reactiveui/reactiveui/releases)
- [Commits](reactiveui/ReactiveUI@18.4.26...19.2.1)

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

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

Author: dependabot[bot]

src/ReactiveMarbles.CacheDatabase.Settings.Tests/ReactiveMarbles.CacheDatabase.Settings.Tests.csproj

@@ -21,7 +21,7 @@
     </PackageReference>
     <PackageReference Include="FluentAssertions" Version="6.11.0" />
     <PackageReference Include="Microsoft.Reactive.Testing" Version="5.0.0" />
-    <PackageReference Include="ReactiveUI.Testing" Version="18.4.26" />
+    <PackageReference Include="ReactiveUI.Testing" Version="19.2.1" />
   </ItemGroup>
 
   <ItemGroup>

src/ReactiveMarbles.CacheDatabase.Tests/ReactiveMarbles.CacheDatabase.Tests.csproj

@@ -23,7 +23,7 @@
     </PackageReference>
     <PackageReference Include="FluentAssertions" Version="6.11.0" />
     <PackageReference Include="Microsoft.Reactive.Testing" Version="5.0.0" />
-    <PackageReference Include="ReactiveUI.Testing" Version="18.4.26" />
+    <PackageReference Include="ReactiveUI.Testing" Version="19.2.1" />
   </ItemGroup>
 
   <ItemGroup>