Fix compilation errors

Author: yim-lee

Sources/ActorSingletonPlugin/ActorSingletonManager.swift

@@ -55,7 +55,7 @@ internal distributed actor ActorSingletonManager<Act: DistributedActor> where Ac
     }
 
     func takeOver(from: UniqueNode?) async throws -> Act {
-        self.log.debug("Take over singleton [\(self.settings.name)] from [\(optional: from)]", metadata: self.metadata())
+        self.log.debug("Take over singleton [\(self.settings.name)] from [\(String(describing: from))]", metadata: self.metadata())
 
         // TODO: (optimization) tell `ActorSingletonManager` on `from` node that this node is taking over (https://github.com/apple/swift-distributed-actors/issues/329)
         let singleton = try await _Props.$forSpawn.withValue(self.singletonProps._knownAs(name: self.settings.name)) {
@@ -66,7 +66,7 @@ internal distributed actor ActorSingletonManager<Act: DistributedActor> where Ac
     }
 
     func handOver(to: UniqueNode?) throws {
-        self.log.debug("Hand over singleton [\(self.settings.name)] to [\(optional: to)]", metadata: self.metadata())
+        self.log.debug("Hand over singleton [\(self.settings.name)] to [\(String(describing: to))]", metadata: self.metadata())
 
         // TODO: (optimization) tell `ActorSingletonManager` on `to` node that this node is handing off (https://github.com/apple/swift-distributed-actors/issues/329)
         self.singleton = nil