build(deps): bump xunit from 2.6.4 to 2.6.6 in /src (#890)

Bumps [xunit](https://github.com/xunit/xunit) from 2.6.4 to 2.6.6.
- [Commits](xunit/xunit@2.6.4...2.6.6)

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

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

src/Akavache.Tests/Akavache.Tests.csproj

@@ -14,7 +14,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
     <PackageReference Include="Microsoft.Reactive.Testing" Version="6.0.0" />
-    <PackageReference Include="xunit" Version="2.6.4" />
+    <PackageReference Include="xunit" Version="2.6.6" />
     <PackageReference Include="xunit.runner.console" Version="2.6.4" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.6" />
     <PackageReference Include="Xunit.SkippableFact" Version="1.4.13" />