fix doc string formatting errors for ExtensionArray.shift issue #28685

Author: HughKelley

pandas/core/arrays/base.py

@@ -540,13 +540,14 @@ def shift(self, periods: int = 1, fill_value: object = None) -> ABCExtensionArra
 
         fill_value : object, optional
             The scalar value to use for newly introduced missing values.
-            The default is ``self.dtype.na_value``
+            The default is ``self.dtype.na_value``.
 
             .. versionadded:: 0.24.0
 
         Returns
         -------
-        shifted : ExtensionArray
+            ExtensionArray
+                Shifted.
 
         Notes
         -----