Fix incorrect MSC3890 unstable prefix (#2703)

Author: Germain

src/@types/event.ts

@@ -210,13 +210,13 @@ export const PUSHER_DEVICE_ID = new UnstableValue(
     "org.matrix.msc3881.device_id");
 
 /**
- * https://github.com/matrix-org/matrix-doc/pull/3881
+ * https://github.com/matrix-org/matrix-doc/pull/3890
  *
  * @experimental
  */
 export const LOCAL_NOTIFICATION_SETTINGS_PREFIX = new UnstableValue(
     "m.local_notification_settings",
-    "m.msc3890.local_notification_settings");
+    "org.matrix.msc3890.local_notification_settings");
 
 export interface IEncryptedFile {
     url: string;