build(deps): bump ReactiveUI from 18.2.9 to 18.3.1 in /src

Bumps [ReactiveUI](https://github.com/reactiveui/reactiveui) from 18.2.9 to 18.3.1.
- [Release notes](https://github.com/reactiveui/reactiveui/releases)
- [Commits](reactiveui/ReactiveUI@18.2.9...18.3.1)

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

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

src/ReactiveUI.DI.Tests/ReactiveUI.DI.Tests.csproj

@@ -28,7 +28,7 @@
   </Choose>
 
   <ItemGroup>
-    <PackageReference Include="ReactiveUI" Version="18.2.9" />
+    <PackageReference Include="ReactiveUI" Version="18.3.1" />
   </ItemGroup>
 
   <ItemGroup>