PPF-688: back to old syntax

Author: chinapandaman

PyPDFForm/middleware/checkbox.py

@@ -34,7 +34,7 @@ def schema_definition(self) -> dict:
         return {"type": "boolean"}
 
     @property
-    def sample_value(self) -> bool | int:
+    def sample_value(self) -> Union[bool, int]:
         """Sample value of the checkbox."""
 
         return True