How to categorize this PR?

/area control-plane
/kind bug

What this PR does / why we need it:

A wrong Shoot configuration can cause the provider extension to not be able to create the MachineClasses or MachineDeployments. The errors that are thrown in this case are on the Worker resource, but are not propagated to the Shoot. The Shoot reconciliation is instead waiting for a timeout and then shows the generic worker status machineDeployments has not been updated error. This error does not help find the wrong configuration in the Shoot.

With this fix the errors in the Worker resource should be propagated to the Shoot immediately to help the user find the wrong configuration.

Ideally the provider extensions catch invalid configurations in the validating admission webhook. This fix is still useful in cases where the required validation is missing.

Which issue(s) this PR fixes:
Partially fixes #12611

Special notes for your reviewer:

i also thought about using

if err := health.CheckExtensionObject(obj); err != nil {
    return err
}

but that is waiting until all MachineDeployments are reconciled and the LastOperation succeeded. This is not what is wanted in this status check method, so I'm only checking for errors instead.

Release note:

Errors that occur during `Worker` reconciliation are now also propagated to the `Shoot` status.