build(deps): bump xunit from 2.7.0 to 2.8.0 in /dotnet (#299)

Bumps [xunit](https://github.com/xunit/xunit) from 2.7.0 to 2.8.0.
- [Commits](xunit/xunit@2.7.0...2.8.0)

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

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

dotnet/test/StackExchange.StacksIcons.Test.csproj

@@ -10,7 +10,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.9.0" />
-    <PackageReference Include="xunit" Version="2.7.0" />
+    <PackageReference Include="xunit" Version="2.8.0" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.8.0">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>