MIG `listManagedInstances` fails to be added

[nsilve]

Description

When we are trying to add listManagedInstances, an error is returned

$ make                                                                                                                                                                                                                                go run pkg/cloud/gen/main.go > pkg/cloud/gen.go
panic: template: interface:34:9: executing "interface" at <.Methods>: error calling Methods: method "InstanceGroupManagers"."ListManagedInstances": paged return type "InstanceGroupManagersListManagedInstancesResponse" does not have a .Items field

goroutine 1 [running]:
main.genTypes({0x2641ba0, 0xc0001103f0})
        /Users/nsilve/IdeaProjects/github/k8s-cloud-provider/pkg/cloud/gen/main.go:1069 +0x187
main.main()
        /Users/nsilve/IdeaProjects/github/k8s-cloud-provider/pkg/cloud/gen/main.go:1447 +0xcc
exit status 2
make: *** [gen] Error 1

because for paged responses an Items field is expected but listManagedInstances returns a managedInstances one.