bpo-39153: Clarify C API *SetItem refcounting semantics (GH-18220)

Some of the *SetItem methods in the C API steal a reference to the
given value. This annotates the better behaved ones to assure the
reader that these are not the ones with the inconsistent behaviour.

* 📜🤖 Added by blurb_it.

* make docs consistent with signature

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
diff --git a/Doc/c-api/object.rst b/Doc/c-api/object.rst
index ca9db1a..2905fbb 100644
--- a/Doc/c-api/object.rst
+++ b/Doc/c-api/object.rst
@@ -331,7 +331,8 @@
 
    Map the object *key* to the value *v*.  Raise an exception and
    return ``-1`` on failure; return ``0`` on success.  This is the
-   equivalent of the Python statement ``o[key] = v``.
+   equivalent of the Python statement ``o[key] = v``.  This function *does
+   not* steal a reference to *v*.
 
 
 .. c:function:: int PyObject_DelItem(PyObject *o, PyObject *key)