[minibuffer] Fix "Invalid preview key" message in minibuffer

[c6c7]

The consult-customize function will now report a message when using (kbd ...) as a value for the :preview-key.

See https://github.com/doomemacs/doomemacs/issues/7064.

[purcell]

Great, thank you — I saw this error but hadn't had time to investigate yet.