Bump FSharp.Core, FsUnit, Microsoft.NETFramework.ReferenceAssemblies and NUnit

Bumps [FSharp.Core](https://github.com/dotnet/fsharp), [FsUnit](https://github.com/fsprojects/FsUnit), [Microsoft.NETFramework.ReferenceAssemblies](https://github.com/Microsoft/dotnet) and [NUnit](https://github.com/nunit/nunit). These dependencies needed to be updated together.

Updates `FSharp.Core` from 8.0.100 to 5.0.2
- [Release notes](https://github.com/dotnet/fsharp/releases)
- [Changelog](https://github.com/dotnet/fsharp/blob/main/release-notes.md)
- [Commits](https://github.com/dotnet/fsharp/commits)

Updates `FsUnit` from 5.3.0 to 5.6.1
- [Release notes](https://github.com/fsprojects/FsUnit/releases)
- [Changelog](https://github.com/fsprojects/FsUnit/blob/master/RELEASE_NOTES.md)
- [Commits](fsprojects/FsUnit@5.3.0...5.6.1)

Updates `Microsoft.NETFramework.ReferenceAssemblies` from 1.0.3 to 1.0.3
- [Commits](https://github.com/Microsoft/dotnet/commits)

Updates `NUnit` from 3.13.3 to 3.14.0
- [Release notes](https://github.com/nunit/nunit/releases)
- [Changelog](https://github.com/nunit/nunit/blob/v3.14.0/CHANGES.md)
- [Commits](nunit/nunit@v3.13.3...v3.14.0)

---
updated-dependencies:
- dependency-name: FSharp.Core
  dependency-type: direct:production
  update-type: version-update:semver-major
- dependency-name: FsUnit
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: Microsoft.NETFramework.ReferenceAssemblies
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: NUnit
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

src/FSharp.Tests/FSharp.Tests.fsproj

@@ -34,10 +34,10 @@
         <Compile Include="Main.fs" />
     </ItemGroup>
     <ItemGroup>
-        <PackageReference Include="NUnit" Version="3.13.3" />
+        <PackageReference Include="NUnit" Version="3.14.0" />
         <PackageReference Include="NUnit3TestAdapter" Version="4.5.0" />
-        <PackageReference Include="NUnitLite" Version="3.13.3" />
-        <PackageReference Include="FsUnit" Version="5.3.0" />
+        <PackageReference Include="NUnitLite" Version="3.14.0" />
+        <PackageReference Include="FsUnit" Version="5.6.1" />
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.9.0" />
         <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.3">
             <PrivateAssets>all</PrivateAssets>