Correct minor gramatical mistake in sys.settrace doc (GH-15637)

Doc/library/sys.rst

@@ -1253,7 +1253,8 @@ always available.
 
    The trace function is invoked (with *event* set to ``'call'``) whenever a new
    local scope is entered; it should return a reference to a local trace
-   function to be used that scope, or ``None`` if the scope shouldn't be traced.
+   function to be used for the new scope, or ``None`` if the scope shouldn't be
+   traced.
 
    The local trace function should return a reference to itself (or to another
    function for further tracing in that scope), or ``None`` to turn off tracing