[3.14] gh-101888: Add function.__builtins__ to ref documentation (GH-144174) (#144252)

gh-101888: Add function.__builtins__ to ref documentation (GH-144174)
(cherry picked from commit 933540e)

Co-authored-by: Victor Stinner <vstinner@python.org>

Author: miss-islington

Doc/reference/datamodel.rst

@@ -546,6 +546,7 @@ Special read-only attributes
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 .. index::
+   single: __builtins__ (function attribute)
    single: __closure__ (function attribute)
    single: __globals__ (function attribute)
    pair: global; namespace
@@ -556,6 +557,12 @@ Special read-only attributes
    * - Attribute
      - Meaning
 
+   * - .. attribute:: function.__builtins__
+     - A reference to the :class:`dictionary <dict>` that holds the function's
+       builtins namespace.
+
+       .. versionadded:: 3.10
+
    * - .. attribute:: function.__globals__
      - A reference to the :class:`dictionary <dict>` that holds the function's
        :ref:`global variables <naming>` -- the global namespace of the module