Bump Microsoft.CSharp in /nuget/helpers/lib/NuGetUpdater

Bumps [Microsoft.CSharp](https://github.com/dotnet/corefx) from 4.3.0 to 4.7.0.
- [Release notes](https://github.com/dotnet/corefx/releases)
- [Commits](https://github.com/dotnet/corefx/commits)

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

Signed-off-by: dependabot[bot] <[email protected]>

nuget/helpers/lib/NuGetUpdater/NuGetProjects/Directory.Packages.props

@@ -5,7 +5,7 @@
     <MicrosoftExtensionsFileProvidersAbstractionsPackageVersion>6.0.0</MicrosoftExtensionsFileProvidersAbstractionsPackageVersion>
     <MicrosoftExtensionsFileSystemGlobbingPackageVersion>9.0.0</MicrosoftExtensionsFileSystemGlobbingPackageVersion>
     <MicrosoftWebXdtPackageVersion>3.0.0</MicrosoftWebXdtPackageVersion>
-    <SystemPackagesVersion>4.3.0</SystemPackagesVersion>
+    <SystemPackagesVersion>4.7.0</SystemPackagesVersion>
     <CryptographyPackagesVersion>5.0.0</CryptographyPackagesVersion>
   </PropertyGroup>