Bump FsUnit from 5.4.0 to 5.6.0

Bumps [FsUnit](https://github.com/fsprojects/FsUnit) from 5.4.0 to 5.6.0.
- [Release notes](https://github.com/fsprojects/FsUnit/releases)
- [Changelog](https://github.com/fsprojects/FsUnit/blob/master/RELEASE_NOTES.md)
- [Commits](fsprojects/FsUnit@5.4.0...5.6.0)

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

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

Author: dependabot[bot]

Directory.Packages.props

@@ -20,7 +20,7 @@
     <PackageVersion Include="System.Memory" Version="4.5.5" />
     <PackageVersion Include="Microsoft.CodeAnalysis.CSharp" Version="4.7.0" />
     <PackageVersion Include="NUnit" Version="3.13.3" />
-    <PackageVersion Include="FsUnit" Version="5.4.0" />
+    <PackageVersion Include="FsUnit" Version="5.6.0" />
     <PackageVersion Include="FSharp.Data" Version="6.3.0" />
     <PackageVersion Include="NUnit3TestAdapter" Version="4.5.0" />
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.7.2" />