Can't change CMake generator

When manually adding a Kit, the CMake Generator can be set to another value. This value isn't being used when building, instead Ninja is used.

When restarting the app, the CMake Generator value is reset to Ninja.

Steps to reproduce:

• Go to Edit > Preferences > Kits > Kits
• Add a Kit
• Change the CMake generator to another value
• Apply changes
• Restart the app and check the value