updated face with face-attribute for unspecified.

[jduhamel]

in mixed pitch mode, :height for the default face was returning unspecified as per emacs29 faces. changed to use face-attribute with inherit.

[rnkn]

Hi Joe,

Here the variable height is supposed to return nil unless the default face has been remapped, in which case it returns the remapped :height property. Your change makes it return the default height of the default face regardless of remapping, which is not what we want. Also I'm not sure if you tested this because when I test it breaks the specified body width.