[expr.ass] Fix typo, "~" should be "^".

This was a misapplication of P2327R1 in 0aebf5c.

Author: tkoeppe

source/expressions.tex

@@ -7168,7 +7168,7 @@
 Such expressions are deprecated
 if \tcode{E1} has volatile-qualified type
 and \placeholder{op} is not one of the bitwise operators
-\tcode{|}, \tcode{\&}, \tcode{\~}; see~\ref{depr.volatile.type}.
+\tcode{|}, \tcode{\&}, \tcode{\^}; see~\ref{depr.volatile.type}.
 For \tcode{+=} and \tcode{-=},
 \tcode{E1} shall either have arithmetic type or be a pointer to a
 possibly cv-qualified completely-defined object type. In all other