build(deps): bump xunit from 2.9.0 to 2.9.1 in /responders/src/API

Bumps [xunit](https://github.com/xunit/xunit) from 2.9.0 to 2.9.1.
- [Commits](xunit/xunit@2.9.0...2.9.1)

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

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

responders/src/API/EMBC.Tests.Unit.Responders.API/EMBC.Tests.Unit.Responders.API.csproj

@@ -13,7 +13,7 @@
     <PackageReference Include="FakeItEasy" Version="8.3.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.10.0" />
     <PackageReference Include="Shouldly" Version="4.2.1" />
-    <PackageReference Include="xunit" Version="2.9.0" />
+    <PackageReference Include="xunit" Version="2.9.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>