🌱 Add linter to show nil panic.

[guettli]

It makes sense to merge #1958 first, because currently unit-tests fail on v1.1.x.

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The code contained an obvious nil panic on err.Error()

		err = action.Error()
		if err != nil {
			err = fmt.Errorf("action %+v failed (wait for rescue enabled): %w", action, err)
			s.scope.Error(err, "")
			err := s.scope.SetErrorAndRemediate(ctx, err.Error())
			if err != nil {
				return reconcile.Result{}, err
			}
			conditions.MarkFalse(hm, infrav1.ServerProvisionedCondition,
				"EnablingRescueActionFailed", clusterv1.ConditionSeverityWarning,
				"%s", err.Error())
			return reconcile.Result{}, nil
		}

No linter complained up to now.

Govet nilness does detect that now.