Clang Release Notes: Fix reST formatting

Fix a use of inline code markup to have a non-word character after the ending delimiter as required by reST.

clang/docs/ReleaseNotes.rst

@@ -68,7 +68,7 @@ AST Dumping Potentially Breaking Changes
 
 Clang Frontend Potentially Breaking Changes
 -------------------------------------------
-- Removed support for constructing on-stack ``TemplateArgumentList``s; interfaces should instead
+- Removed support for constructing on-stack ``TemplateArgumentList``\ s; interfaces should instead
   use ``ArrayRef<TemplateArgument>`` to pass template arguments. Transitioning internal uses to
   ``ArrayRef<TemplateArgument>`` reduces AST memory usage by 0.4% when compiling clang, and is
   expected to show similar improvements on other workloads.