Bump ServiceStack in /Samples/ServiceAPI/CSharp/GoogleAuthPlugin

Bumps [ServiceStack](https://github.com/ServiceStack/ServiceStack) from 4.5.14 to 5.9.2.
- [Release notes](https://github.com/ServiceStack/ServiceStack/releases)
- [Commits](ServiceStack/ServiceStack@v4.5.14...v5.9.2)

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

Author: dependabot[bot]

Samples/ServiceAPI/CSharp/GoogleAuthPlugin/packages.config

@@ -4,7 +4,7 @@
   <package id="Microsoft.Bcl" version="1.1.10" targetFramework="net45" />
   <package id="Microsoft.Bcl.Build" version="1.0.14" targetFramework="net45" />
   <package id="Microsoft.Net.Http" version="2.2.29" targetFramework="net45" />
-  <package id="ServiceStack" version="4.5.14" targetFramework="net45" />
+  <package id="ServiceStack" version="5.9.2" targetFramework="net45" />
   <package id="ServiceStack.Authentication.OAuth2" version="4.5.14" targetFramework="net45" />
   <package id="ServiceStack.Client" version="4.5.14" targetFramework="net45" />
   <package id="ServiceStack.Common" version="4.5.14" targetFramework="net45" />