PostgreSQL 18 stores NOT NULL constraints in pg_constraint (with

contype='n'). Django's get_constraints() includes these in its

results, but with all type flags (index, unique, primary_key, check,

foreign_key) set to False. get_constraints_for_table() was passing

through all constraint entries unconditionally, causing these NOT NULL

constraints to be tracked as regular non-unique indexes in

DatabaseState (e.g., "tests_testmodel_int_field1_not_null").
This caused two categories of failures:


ChangeField operations that modified db_index or unique would

   find unexpected NOT NULL indexes in the database state, causing

   assertion failures.


ChangeMeta(indexes) operations would see NOT NULL constraint

   entries instead of the actual Django-managed indexes, generating

   incorrect DROP/CREATE INDEX SQL.


The fix filters get_constraints_for_table() to only include entries

where index, unique, or primary_key is True. This excludes NOT NULL

constraints, check constraints, and foreign key constraint entries --

none of which should be tracked as indexes in DatabaseState. (Foreign

key fields still have their actual indexes captured via separate

index=True entries, and check constraints are handled through Django's

Meta.constraints system.)

Ran dbtests-minmax