ban-drop-constraint
problem
Dropping a table, foreign table, or domain constraint, or setting a table constraint to NOT ENFORCED, removes a guarantee that clients can depend on. If an old application uses INSERT ... ON CONFLICT ON CONSTRAINT c or infers a dropped unique constraint as its conflict arbiter, its inserts fail immediately. This rule is enabled by default.
alter table t drop constraint if exists c;
solution
Update clients to not depend on the constraint before dropping it.
Exclude this rule with --exclude ban-drop-constraint after checking application compatibility.