tests: only record failed tests in integration_tests.json

The file gets too big otherwise - it becomes hard to search through to find the failed cases.

See https://nomadic-labs.gitlab.io/-/tezos-ledger-app-revamp/-/jobs/4487221567/artifacts/integration_tests.json for example, it's empty 😄 ( and https://nomadic-labs.gitlab.io/-/tezos-ledger-app-revamp/-/jobs/4487221571/artifacts/integration_tests.json for an example only containing test failures)