Description of the problem:

The env has 1 managedclusters, belongs to both global clustersets, and global clustersets binds to namespace open-cluster-management-global-set.
```
$ clusteradm get clusters
NAME       ACCEPTED   AVAILABLE   CLUSTERSET   CPU   MEMORY       KUBERNETES VERSION
cluster1   true       True        default      24    49265492Ki   v1.23.4

$ clusteradm get clustersets
NAME      BOUND NAMESPACES                     STATUS
default                                        1 ManagedClusters selected
global    open-cluster-management-global-set   1 ManagedClusters selected
```

Create placement under namespace open-cluster-management-global-set, 1 cluster selected.
```
$ cat placement.yaml
apiVersion: cluster.open-cluster-management.io/v1beta1
kind: Placement
metadata:
  name: demo-placement
  namespace: open-cluster-management-global-set
spec:
  predicates:
  - requiredClusterSelector:
      labelSelector:
        matchExpressions:
        - key: name
          operator: NotIn
          values:
          - local-clusterr
  tolerations:
  - key: cluster.open-cluster-management.io/unreachable
    operator: Exists

$ oc create -f placement.yaml
placement.cluster.open-cluster-management.io/demo-placement created

$ oc get placement -A
NAMESPACE                            NAME             SUCCEEDED   REASON                  SELECTEDCLUSTERS
open-cluster-management-global-set   demo-placement   True        AllDecisionsScheduled   1
```

Add new cluster cluster2, it also belongs to global clusterset.
```
$ cat cluster2.yaml
apiVersion: cluster.open-cluster-management.io/v1
kind: ManagedCluster
metadata:
  name: cluster2
spec:
  hubAcceptsClient: true
  leaseDurationSeconds: 60
$ oc create -f cluster2.yaml
managedcluster.cluster.open-cluster-management.io/cluster2 created

$ clusteradm get clusters
NAME       ACCEPTED   AVAILABLE   CLUSTERSET   CPU   MEMORY       KUBERNETES VERSION
cluster1   true       True        default      24    49265492Ki   v1.23.4
cluster2   true       Unknown     default

$ clusteradm get clustersets
NAME      BOUND NAMESPACES                     STATUS
default                                        2 ManagedClusters selected
global    open-cluster-management-global-set   2 ManagedClusters selected
```

However, the placement decision didn't update, and only 1 cluster was selected.
```
$ oc get placement -A
NAMESPACE                            NAME             SUCCEEDED   REASON                  SELECTEDCLUSTERS
open-cluster-management-global-set   demo-placement   True        AllDecisionsScheduled   1
```

Release version:
2.6

Operator snapshot version:

OCP version:

Browser Info:

Steps to reproduce:
1.
2.
3.

Actual results:

Expected results:
Both of the 2 clusters were selected.
```
$ oc get placement -A
NAMESPACE                            NAME             SUCCEEDED   REASON                  SELECTEDCLUSTERS
open-cluster-management-global-set   demo-placement   True        AllDecisionsScheduled   2
```

Additional info: