AttributeError: 'DatasetInfo' object has no attribute 'task_templates'
Hi ! Can you try using a more up-to-date version ? We added the task_templates in `datasets` 1.7.0.

Ideally when you're working on new datasets, you should install and use the local version of your fork of `datasets`. Here I think you tried to run the 1.7.0 tests with the 1.6.2 code
## Describe the bug
Hello, 
I'm trying to add dataset and contribute, but test keep fail with below cli.
` RUN_SLOW=1 pytest tests/test_dataset_common.py::LocalDatasetTest::test_load_dataset_all_configs_<my_dataset>`

## Steps to reproduce the bug
It seems like a bug when I see an error with the existing dataset, not the dataset I'm trying to add.

` RUN_SLOW=1 pytest tests/test_dataset_common.py::LocalDatasetTest::test_load_dataset_all_configs_<any_dataset>`


## Expected results
All test passed

## Actual results
```
                # check that dataset is not empty
                self.parent.assertListEqual(sorted(dataset_builder.info.splits.keys()), sorted(dataset))
                for split in dataset_builder.info.splits.keys():
                    # check that loaded datset is not empty
                    self.parent.assertTrue(len(dataset[split]) > 0)
    
                # check that we can cast features for each task template
>               task_templates = dataset_builder.info.task_templates
E               AttributeError: 'DatasetInfo' object has no attribute 'task_templates'

tests/test_dataset_common.py:175: AttributeError
```


## Environment info
<!-- You can run the command `datasets-cli env` and copy-and-paste its output below. -->
- `datasets` version: 1.6.2
- Platform: Darwin-20.4.0-x86_64-i386-64bit
- Python version: 3.7.7
- PyTorch version (GPU?): 1.7.0 (False)
- Tensorflow version (GPU?): 2.3.0 (False)
- Using GPU in script?: No
- Using distributed or parallel set-up in script?: No
