Require psycopq >=3.3

I tried importing some data to an ixmp4 database (via DirectTransport), but I got a strange error messages about not being able to cast an INT64 to an integer using %s. I had psycopg v3.1 in line with the requirements, but the issue was resolved by installing the latest version.

@meksor, can you please take a look at some point and check if the requirements need to be bumped? (or if this was just some strange dependency-interaction on my computer).