Handle error returned by GetClusterInfos() (#30919)

A recent change to the enterprise cluster code introduced a change to the enterprise API interface. GetClusterInfos() can now return an error. This commit introduces code to handle that error.

server/channels/jobs/batch_migration_worker_test.go

@@ -20,8 +20,8 @@ type MockApp struct {
 	clusterInfo []*model.ClusterInfo
 }
 
-func (ma MockApp) GetClusterStatus(rctx request.CTX) []*model.ClusterInfo {
-	return ma.clusterInfo
+func (ma MockApp) GetClusterStatus(rctx request.CTX) ([]*model.ClusterInfo, error) {
+	return ma.clusterInfo, nil
 }
 
 func (ma *MockApp) SetInSync() {