(maint): Bump xunit from 2.4.2 to 2.6.0

Bumps [xunit](https://github.com/xunit/xunit) from 2.4.2 to 2.6.0.
- [Commits](xunit/xunit@2.4.2...2.6.0)

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

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

src/Cake.FileHelpers.Tests/Cake.FileHelpers.Tests.csproj

@@ -8,7 +8,7 @@
  <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
  <PrivateAssets>all</PrivateAssets>
  </PackageReference>
- <PackageReference Include="xunit" Version="2.4.2" />
+ <PackageReference Include="xunit" Version="2.6.0" />
  <PackageReference Include="xunit.runner.visualstudio" Version="2.4.5" />
  <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.6.3" />
  </ItemGroup>