Bump xunit from 2.5.3 to 2.6.1 (#98)

Bumps [xunit](https://github.com/xunit/xunit) from 2.5.3 to 2.6.1.
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/xunit/xunit/commit/9f1684f5f74196d952f0085d7bde21aa20df6229"><code>9f1684f</code></a>
v2.6.1</li>
<li><a
href="https://github.com/xunit/xunit/commit/5d9ef4b8ef82e3e3a8581a259f8a02fb01fd7391"><code>5d9ef4b</code></a>
Remove unnecessary XUNIT_VALUETASK definition</li>
<li><a
href="https://github.com/xunit/xunit/commit/0266bac5ed8b31ada11b6034c9fe013142090033"><code>0266bac</code></a>
Latest assertions</li>
<li><a
href="https://github.com/xunit/xunit/commit/fb3c3cf30445dc5a7aa7fdca6fe8118dc407b960"><code>fb3c3cf</code></a>
Remove all ValueTask support from assertions</li>
<li><a
href="https://github.com/xunit/xunit/commit/801790c5accbaa51b06fde9397b92a47d4ae8f41"><code>801790c</code></a>
Reconcile AcceptanceTestAssembly and friends with v3</li>
<li><a
href="https://github.com/xunit/xunit/commit/f244cc89bf086ce8a3b3f628f70da14e2420a4a4"><code>f244cc8</code></a>
More shared assertion tests that shouldn't return ValueTask</li>
<li><a
href="https://github.com/xunit/xunit/commit/262dd72145a7a62143926892beab0af1f9832e9e"><code>262dd72</code></a>
Shared assertion tests cannot return ValueTask</li>
<li><a
href="https://github.com/xunit/xunit/commit/36bbf773ea60b1fa1622063c160cfb4b0707dcd8"><code>36bbf77</code></a>
Bump up to v2.6.1-pre</li>
<li><a
href="https://github.com/xunit/xunit/commit/6a07b9530d643f938287db600feb46082e894188"><code>6a07b95</code></a>
v2.6.0</li>
<li><a
href="https://github.com/xunit/xunit/commit/5a7297e8dcbc7998dc85708af8fb3756888ccd14"><code>5a7297e</code></a>
<a href="https://redirect.github.com/xunit/xunit/issues/2806">#2806</a>:
Performance improvements in Assert.Equal (v2)</li>
<li>Additional commits viewable in <a
href="https://github.com/xunit/xunit/compare/2.5.3...2.6.1">compare
view</a></li>
</ul>
</details>
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Directory.Packages.props

@@ -8,7 +8,7 @@
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.7.2" />
     <PackageVersion Include="Microsoft.SourceLink.GitHub" Version="1.1.1" />
     <PackageVersion Include="Moq" Version="4.20.69" />
-    <PackageVersion Include="xunit" Version="2.5.3" />
+    <PackageVersion Include="xunit" Version="2.6.1" />
     <PackageVersion Include="xunit.runner.visualstudio" Version="2.5.3" />
   </ItemGroup>
 </Project>