I have found a solution, but it is not such that you can use it in the source code:
For the server producing the error referred to above, I added
newpgtype(:text, 107980182, ()) to types.jl
on another computer the oid (object id) for citext is 427189 and on a third one 30652.
The next step would be to let the driver looks up the oid for citext with a query like this:
select oid from pg_type where typname = 'citext';
and add the correct
newpgtype to the code.