serializers: Deserialize as lists instead of tuples
- for consistency with the serializers in swh.core
- it's not clear to me that we ever needed that (it was added in rDJNL64cd01fc with no rational)
- it messes with swh-search reading from the journal and expecting JSON-like data. (T2876#54729)
Test Plan
Tests will fail because of https://github.com/msgpack/msgpack-python/issues/451
Migrated from D4758 (view on Phabricator)