When constructing a UniqueConstraint, several attributes (fields,

include, expressions) get converted from a list to a tuple.
When deserializing a UniqueConstraint from JSON, those attributes come

in as a list.
The resulting ConstraintSignature takes on the types used from either

the constructed or deserialized object. Due to these type differences,

this means two constraints never compare to the same value, even if they

have the same content.
To address this, we now normalize the attributes to convert any tuples

to lists for the signature representation, allowing them to compare

equally.

Unit tests pass with all versions of Django.
Tested that this fixed an upgrade condition I dealt with locally

during development.