[expr.const] Add non-breaking space after \cv (#7710)

Author: cpplearner

source/expressions.tex

@@ -8033,7 +8033,7 @@
 it is applied to
 \begin{itemize}
   \item
-  a glvalue of type \cv \tcode{std::nullptr_t},
+  a glvalue of type \cv{}~\tcode{std::nullptr_t},
 
   \item
   a non-volatile glvalue that refers to an object that is