fix an incorrect role

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

Author: AA-Turner

peps/pep-0781.rst

@@ -29,7 +29,7 @@ Type annotations were defined for Python by :pep:`484`, and have enjoyed
 widespread adoption. A challenge with fully-annotated code is that many
 more imports are required in order to bring the relevant name into scope,
 potentially causing import cycles without careful design. This has been
-recognized by :pep:`563` and later :pep`649`, which introduce two different
+recognized by :pep:`563` and later :pep:`649`, which introduce two different
 mechanisms for deferred evaluation of type annotations. As :pep:`!563` notes,
 "type hints are ... not computationally free". The :data:`typing.TYPE_CHECKING`
 constant was thus introduced__, initially to aid in breaking cyclic imports.