Using incoherent instances, there can be situations where two
occurrences of the same overloaded function at the same type use two
different instances (see #22448). For incoherently resolved instances,
we must mark them with `nospec` to avoid the specialiser rewriting one
to the other. This marking is done during the desugaring of the
`WpEvApp` wrapper.

Fixes #22448

Metric Increase:
    T15304