The Note in [dcl.fct]/7 says:

A function type that has a cv-qualifier-seq is not a cv-qualified type; there are no cv-qualified function types.

[class.this]/3 says:

A cv-qualified member function can be called on an object-expression only if the object-expression is as cv-qualified or less-cv-qualified than the member function.

I assume «as cv-qualified or less-cv-qualified» means «not more cv-qualified», as defined in [basic.type.qualifier]/4:

There is a partial ordering on cv-qualifiers, so that a type can be said to be more cv-qualified than another. Table 11 shows the relations that constitute this ordering.

If a function type can't be cv-qualified, how could one compare whether a non-stastic member function (type(?)) more or less cv-qualified than an object-expression (type(?))?