Bump FsUnit.xUnit from 5.6.1 to 6.0.0

Bumps [FsUnit.xUnit](https://github.com/fsprojects/FsUnit) from 5.6.1 to 6.0.0.
- [Release notes](https://github.com/fsprojects/FsUnit/releases)
- [Changelog](https://github.com/fsprojects/FsUnit/blob/master/RELEASE_NOTES.md)
- [Commits](fsprojects/FsUnit@5.6.1...6.0.0)

---
updated-dependencies:
- dependency-name: FsUnit.xUnit
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

VaughanTests/VaughanTests.fsproj

@@ -27,6 +27,6 @@
     <PackageReference Include="xunit" Version="2.6.5" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.6" />
     <PackageReference Include="FsCheck.Xunit" Version="2.16.6" />
-    <PackageReference Include="FsUnit.xUnit" Version="5.6.1" />
+    <PackageReference Include="FsUnit.xUnit" Version="6.0.0" />
   </ItemGroup>
 </Project>