Fix backticks

Author: warsaw

peps/pep-0829.rst

@@ -430,7 +430,7 @@ Open Issues
 Change History
 ==============
 
-`TBD`
+``TBD``
 
 * During the deprecation period, warnings about ``import`` lines in
   ``<name>.pth`` files with no matching ``<name>.start`` file are only issued