Bump xunit from 2.5.1 to 2.6.3

Bumps [xunit](https://github.com/xunit/xunit) from 2.5.1 to 2.6.3.
- [Commits](xunit/xunit@2.5.1...2.6.3)

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

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

DeveImageOptimizer.Tests/DeveImageOptimizer.Tests.csproj

@@ -18,7 +18,7 @@
     </PackageReference>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.7.2" />
     <PackageReference Include="System.Memory" Version="4.5.5" />
-    <PackageReference Include="xunit" Version="2.5.1" />
+    <PackageReference Include="xunit" Version="2.6.3" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.1">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>