C++: Update expected test results after frontend _Generic fix

Author: jketema

cpp/ql/test/library-tests/ir/ir/PrintAST.expected

@@ -4343,7 +4343,7 @@ generic.c:
 #    3|                 ValueCategory = prvalue
 #    3|             getAssociationExpr(0): [ReuseExpr] reuse of x
 #    3|                 Type = [IntType] unsigned int
-#    3|                 ValueCategory = lvalue
+#    3|                 ValueCategory = prvalue
 #    3|             getAssociationType(1): [TypeName] int
 #    3|                 Type = [IntType] int
 #    3|                 ValueCategory = prvalue