Payment term's PaymentTermLineRelativeDelta does too many migration
In order to fix #7962 (closed) we introduced a change that drop and recreate the columns month and weekday even if there is no migration to handle.
When executing the migration a great number of time we reach the maximum number of column permitted on a postgresql because postgres never removes the dropped column but hides it: https://nerderati.com/2017/01/03/postgresql-tables-can-have-at-most-1600-columns/
I propose to add to the backend table handler a way to retrieve the column type and change the test to check if the column should be dropped or not.