add __invert__

Author: MarcoGorelli

spec/API_specification/dataframe_api/dataframe_object.py

@@ -418,6 +418,12 @@ def __divmod__(self, other: DataFrame | Scalar) -> tuple[DataFrame, DataFrame]:
         """
         ...
 
+    def __invert__(self) -> DataFrame:
+        """
+        Invert truthiness of (boolean) elements.
+        """
+        ...
+
     def any(self, skipna: bool = True) -> DataFrame:
         """
         Reduction returns a 1-row DataFrame.