free5GC is an open-source implementation of the 5G core network. Prior to 4.2.2, free5GC's BSF PUT /nbsf-management/v1/subscriptions/{subId} handler has an unsynchronized write on the global Subscriptions map. The handler first reads the map under RLock() via BSFContext.GetSubscription(subId), but if the subscription does not exist, ReplaceIndividualSubcription() writes back to the same map direct

### Summary free5GC's BSF `PUT /nbsf-management/v1/subscriptions/{subId}` handler has an unsynchronized write on the global `Subscriptions` map. The handler first reads the map under `RLock()` via `BSFContext.GetSubscription(subId)`, but if the subscription does not exist, `ReplaceIndividualSubcription()` writes back to the same map directly without taking the mutex (`bsfContext.BsfSelf.Subscripti