events: change type of state_key field of HierarchySpaceChildEvent to OwnedRoomId

crates/ruma-events/CHANGELOG.md

@@ -9,6 +9,7 @@ Breaking changes:
   -`RoomPowerLevels::user_can_redact` is split into `user_can_redact_own_event`
     and `user_can_redact_event_of_other`,
   - `PowerLevelAction::Redact` is split into `RedactOwn` and `RedactOther`.
+- Use `OwnedRoomId` instead of `String` for the `state_key` field of `HierarchySpaceChildEvent`
 
 Improvements:
 

crates/ruma-events/src/space/child.rs

@@ -63,7 +63,7 @@ pub struct HierarchySpaceChildEvent {
     pub sender: OwnedUserId,
 
     /// The room ID of the child.
-    pub state_key: String,
+    pub state_key: OwnedRoomId,
 
     /// Timestamp in milliseconds on originating homeserver when this event was sent.
     pub origin_server_ts: MilliSecondsSinceUnixEpoch,