Bump the dev-dependencies group in /tests with 2 updates

Bumps the dev-dependencies group in /tests with 2 updates: [xunit](https://github.com/xunit/xunit) and [xunit.runner.visualstudio](https://github.com/xunit/visualstudio.xunit).


Updates `xunit` from 2.8.1 to 2.9.0
- [Commits](xunit/xunit@2.8.1...2.9.0)

Updates `xunit.runner.visualstudio` from 2.8.1 to 2.8.2
- [Release notes](https://github.com/xunit/visualstudio.xunit/releases)
- [Commits](xunit/visualstudio.xunit@2.8.1...2.8.2)

---
updated-dependencies:
- dependency-name: xunit
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: dev-dependencies
- dependency-name: xunit.runner.visualstudio
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: dev-dependencies
...

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

tests/RiimutTest.csproj

@@ -8,8 +8,8 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.10.0" />
-    <PackageReference Include="xunit" Version="2.8.1" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.1">
+    <PackageReference Include="xunit" Version="2.9.0" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>