Training with a custom service account needs a new field named service account
trainingInput:
  serviceAccount: CUSTOM_SERVICE_ACCOUNT

https://cloud.google.com/ai-platform/training/docs/custom-service-account


tests/providers/google/cloud/operators/test_mlengine.py
TRAINING_DEFAULT_ARGS = {
        'project_id': 'test-project',
        'job_id': 'test_training',
        'package_uris': ['gs://some-bucket/package1'],
        'training_python_module': 'trainer',
        'training_args': '--some_arg=\'aaa\'',
        'region': 'us-east1',
        'scale_tier': 'STANDARD_1',
        'labels': {'some': 'labels'},
        'task_id': 'test-training',
        'start_date': days_ago(1),
    }
    TRAINING_INPUT = {
        'jobId': 'test_training',
        'labels': {'some': 'labels'},
        'trainingInput': {
            'scaleTier': 'STANDARD_1',
            'packageUris': ['gs://some-bucket/package1'],
            'pythonModule': 'trainer',
            'args': '--some_arg=\'aaa\'',
            'region': 'us-east1',
        },
    }
    def setUp(self):