We already show a message when showing an asset library whose path can't be
found on disk. The red text was making it look like some fatal error happened.
And the message could be a bit more useful generally.
So this removes the red color of the text, (arguably) improves the text and
adds a button as shortcut to open the Preferences with the asset library
settings.
Differential Revision: https://developer.blender.org/D12894
ca2ae350ec