Add missing return type

Author: x24git

src/prompt_toolkit/filters/app.py

@@ -178,7 +178,7 @@ def has_any_validation_error() -> bool:
     from prompt_toolkit.layout.controls import UIControl, BufferControl, SearchBufferControl
 
     # Extract buffer validation errors for buffer UIControl children classes
-    def get_buffer_from_content(content: UIControl):
+    def get_buffer_from_content(content: UIControl) -> bool:
         if isinstance(content, (BufferControl, SearchBufferControl)):
             return content.buffer.validation_error is not None
         else: