chore(api): fix overbooked property type hint

api/libretime_api/schedule/models/schedule.py

@@ -52,7 +52,7 @@ class Schedule(models.Model):
     )
 
     @property
-    def overbooked(self):
+    def overbooked(self) -> bool:
         """
         A schedule item is overbooked if it starts after the end of the show
         instance it is in.

api/schema.yml

@@ -6512,7 +6512,7 @@ components:
           type: boolean
           nullable: true
         overbooked:
-          type: string
+          type: boolean
           readOnly: true
     PatchedServiceRegister:
       type: object
@@ -7403,7 +7403,7 @@ components:
           type: boolean
           nullable: true
         overbooked:
-          type: string
+          type: boolean
           readOnly: true
       required:
         - broadcasted