[clang][docs] Fix formatting in breaking changes note

Need to use double backticks to get plain text in RST.

Author: DavidSpickett

clang/docs/ReleaseNotes.rst

@@ -36,7 +36,7 @@ Potentially Breaking Changes
 
 - The Objective-C ARC migrator (ARCMigrate) has been removed.
 - Fix missing diagnostics for uses of declarations when performing typename access,
-  such as when performing member access on a '[[deprecated]]' type alias.
+  such as when performing member access on a ``[[deprecated]]`` type alias.
   (#GH58547)
 - For ARM targets when compiling assembly files, the features included in the selected CPU
   or Architecture's FPU are included. If you wish not to use a specific feature,