PEP 751: add canonical link to spec (#4419)

Author: brettcannon

peps/pep-0751.rst

@@ -12,6 +12,8 @@ Post-History:
 Replaces: 665
 Resolution: `31-Mar-2025 <https://discuss.python.org/t/77293/150>`__
 
+.. canonical-pypa-spec:: :ref:`pylock-toml-spec`
+
 ========
 Abstract
 ========