Bump xunit from 2.5.0 to 2.6.0 (#245)

Bumps [xunit](https://github.com/xunit/xunit) from 2.5.0 to 2.6.0.
- [Commits](xunit/xunit@2.5.0...2.6.0)

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

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

Author: dependabot[bot]

src/Directory.Build.props

@@ -16,7 +16,7 @@ Upgraded to Phobos 2.0.6</PackageReleaseNotes>
   </PropertyGroup>
   <PropertyGroup>
     <LibraryFramework>netstandard2.0</LibraryFramework>
-    <XunitVersion>2.5.0</XunitVersion>
+    <XunitVersion>2.6.0</XunitVersion>
     <XunitRunnerVersion>2.5.3</XunitRunnerVersion>
     <TestSdkVersion>17.6.3</TestSdkVersion>
     <PbmVersion>1.3.2</PbmVersion>