build(deps): update ReactiveUI requirement from 14.* to 15.* in /src (#…

…334)

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@14.1.1...15.1.1)

---
updated-dependencies:
- dependency-name: ReactiveUI
  dependency-type: direct:production
...

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

src/ReactiveUI.Validation/ReactiveUI.Validation.csproj

@@ -9,6 +9,6 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="ReactiveUI" Version="14.*" />
+    <PackageReference Include="ReactiveUI" Version="15.*" />
   </ItemGroup>
 </Project>