Fix PyTrace_RETURN documentation (GH-5384) (GH-5387)

It will be triggered when propagating an exception.
(cherry picked from commit 79db11ce99332d62917be9d03b31494b1ff2f96a)
diff --git a/Doc/c-api/init.rst b/Doc/c-api/init.rst
index f091ac8..229cae5 100644
--- a/Doc/c-api/init.rst
+++ b/Doc/c-api/init.rst
@@ -1030,7 +1030,7 @@
 .. c:var:: int PyTrace_RETURN
 
    The value for the *what* parameter to :c:type:`Py_tracefunc` functions when a
-   call is returning without propagating an exception.
+   call is about to return.
 
 
 .. c:var:: int PyTrace_C_CALL