[3.13] [docs] fix a Sphinx directive in c-api/object.rst (GH-121430) (#121440)

[docs] fix a Sphinx directive in `c-api/object.rst` (GH-121430)
(cherry picked from commit ada964fba0)

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

Doc/c-api/object.rst

@@ -52,6 +52,7 @@ Object Protocol
 
    The reference is borrowed from the interpreter, and is valid until the
    interpreter finalization.
+
    .. versionadded:: 3.13