Fix missing import in dataclass code snippet (GH-29214)

LeoHuckvale · web-flow · commit ad4e8d2b871c · 2022-02-14T12:01:53.000-08:00
field was not imported. It has been added now.
diff --git a/Doc/whatsnew/3.10.rst b/Doc/whatsnew/3.10.rst
@@ -1019,7 +1019,7 @@ You can specify keyword-only on a per-field basis:
 
 .. code-block:: python
 
-    from dataclasses import dataclass
+    from dataclasses import dataclass, field
 
     @dataclass
     class Birthday:
