A recent regression caused ExtensionResource's 'enabled' state to be

incorrect after enabling/disabling an extension. The value would be that

of the old state. This led to an unexpected combination of states in the

extension list, which caused the "Enable", "Disable", etc. actions to

disappear.
The reason this happened is that get_object() now caches results, and

ExtensionResource was attempting to use it in order to reload the

RegisteredExtension instance. We now reload it like all other resources

do, which is to just re-fetch from the database using the existing

instance's ID.

Enabled and disabled extensions. Saw the links appear and reflect the

correct state.
Checked the resulting payload from the API, and it too had the right state.