Update datasets to 2.20.0 (#3040)
* Update datasets to 2.20.0
* Update poetry lock files
* Force CI rerun
* Pass trust_remote_code in external_files_dataset_builder
* Avoid assertion in test_statistics_endpoint failing due to pandas bug
* Force CI rerun
* Revert commented assertion in test_statistics_endpoint
* Create test fixture with JSON-Lines dataset
* Use test fixture with JSON-Lines dataset in test_statistics_endpoint
