fix: deletion of untouched machines

[vknabel]

Description

When trying to delete a metalstackmachine that has not yet been created, it still tried to find it. Resulting in the following error and a deadlock.

capms-controller-manager-8469bcdb77-qntkg manager 2025-03-06T10:52:11Z    ERROR   Reconciler error        {"controller": "metalstackmachine", "controllerGroup": "infrastructure.cluster.x-k8s.io", "controllerKind": "MetalStackMachine", "MetalStackMachine": {"name":"metal-test-md-0-zvdmm-d4m2m","namespace":"default"}, "namespace": "default", "name": "metal-test-md-0-zvdmm-d4m2m", "reconcileID": "0fa4ed89-6f86-4062-b2f4-f32e3defc479", "error": "failed to find provider machine: json: cannot unmarshal array into Go value of type models.V1MachineResponse"}

[Gerrit91]

In general we need to consider that our code can lead to machine leakage. So, maybe we need an orphan detection or something at some point. But this is out of scope of this PR.