chore(deps): update dependency xunit to v2.6.6 (#35)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [xunit](https://togithub.com/xunit/xunit) | `2.6.5` -> `2.6.6` |
[![age](https://developer.mend.io/api/mc/badges/age/nuget/xunit/2.6.6?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
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|
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|
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|

---

### Release Notes

<details>
<summary>xunit/xunit (xunit)</summary>

### [`v2.6.6`](https://togithub.com/xunit/xunit/compare/2.6.5...2.6.6)

[Compare Source](https://togithub.com/xunit/xunit/compare/2.6.5...2.6.6)

</details>

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Server.Tests/Server.Tests.csproj

@@ -14,7 +14,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
-    <PackageReference Include="xunit" Version="2.6.5" />
+    <PackageReference Include="xunit" Version="2.6.6" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.6" />
     <PackageReference Include="Snapshooter.Xunit" Version="0.13.0" />
   </ItemGroup>