Bump ServiceStack in /src/DefaultApp/DefaultApp/DefaultApp.AppMac

Bumps [ServiceStack](https://github.com/ServiceStack/ServiceStack) from 4.5.12 to 5.9.2.
- [Release notes](https://github.com/ServiceStack/ServiceStack/releases)
- [Commits](ServiceStack/ServiceStack@v4.5.12...v5.9.2)

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

src/DefaultApp/DefaultApp/DefaultApp.AppMac/packages.config

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <packages>
-  <package id="ServiceStack" version="4.5.12" targetFramework="net452" />
+  <package id="ServiceStack" version="5.9.2" targetFramework="net452" />
   <package id="ServiceStack.Client" version="4.5.12" targetFramework="net452" />
   <package id="ServiceStack.Common" version="4.5.12" targetFramework="net452" />
   <package id="ServiceStack.Interfaces" version="4.5.12" targetFramework="net452" />