Allow running the prefix validation workflow on out-of-sync subscriptions

gso/workflows/__init__.py

 """Initialisation class that imports all workflows into GSO."""
 
-from orchestrator.services.subscriptions import WF_USABLE_MAP
+from orchestrator.services.subscriptions import WF_USABLE_MAP, WF_USABLE_WHILE_OUT_OF_SYNC
 from orchestrator.types import SubscriptionLifecycle
 from orchestrator.workflows import LazyWorkflowInstance
 
@@ -28,6 +28,8 @@ WF_USABLE_MAP.update({
     "validate_iptrunk": [SubscriptionLifecycle.PROVISIONING, SubscriptionLifecycle.ACTIVE],
 })
 
+WF_USABLE_WHILE_OUT_OF_SYNC.extend(["validate_geant_ip_prefix_list"])
+
 #  IP trunk workflows
 LazyWorkflowInstance("gso.workflows.iptrunk.activate_iptrunk", "activate_iptrunk")
 LazyWorkflowInstance("gso.workflows.iptrunk.create_iptrunk", "create_iptrunk")