chore: bump the dependencies group in /FastActivator.Tests with 1 update

Bumps the dependencies group in /FastActivator.Tests with 1 update: [Mecha.xUnit](https://github.com/JaCraig/Mecha).


Updates `Mecha.xUnit` from 2.1.7 to 2.1.8
- [Changelog](https://github.com/JaCraig/Mecha/blob/main/CHANGELOG.md)
- [Commits](JaCraig/Mecha@v2.1.7...v2.1.8)

---
updated-dependencies:
- dependency-name: Mecha.xUnit
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: dependencies
...

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

FastActivator.Tests/FastActivator.Tests.csproj

@@ -7,7 +7,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Mecha.xUnit" Version="2.1.7" />
+    <PackageReference Include="Mecha.xUnit" Version="2.1.8" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
     <PackageReference Include="xunit" Version="2.6.6" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.6">