Control Plane Machine Set Operator OnDelete update should cause an error when more than one machine is ready in an index

when using the OnDelete update method of the ControlPlaneMachineSet, it should not be possible to have multiple machines in the Running phase in the same machine index. eg, if machine-1 is in Running phase, we should not have a machine-replacement-1 also in the Running phase.

4.12 / main branch

unsure, this is currently not tested in the code and is difficult to produce

1. setup a cluster with CPMS in OnDelete update mode
2. rename one of the master machines to have the same index as another, or manually create a machine to match. this step might be difficult to reproduce.
3. observe logs from CPMS operator

no errors are emitted about the extra machine, although perhaps others are. operator does not degrade.

an error should be produced and the operator should go degraded

this bug is slightly predictive, we have not observed this condition but have detected a gap in the code that might make it possible.