bpo-40429: PyThreadState_GetFrame() returns a strong ref (GH-19781)

The PyThreadState_GetFrame() function now returns a strong reference
to the frame.
diff --git a/Doc/c-api/init.rst b/Doc/c-api/init.rst
index afde3db..68fed2a 100644
--- a/Doc/c-api/init.rst
+++ b/Doc/c-api/init.rst
@@ -1074,10 +1074,10 @@
 
 .. c:function:: PyFrameObject* PyThreadState_GetFrame(PyThreadState *tstate)
 
-   Get a borrowed reference to the current frame of the Python thread state
-   *tstate*.
+   Get the current frame of the Python thread state *tstate*.
 
-   Return ``NULL`` if no frame is currently executing.
+   Return a strong reference. Return ``NULL`` if no frame is currently
+   executing.
 
    See also :c:func:`PyEval_GetFrame`.