NonMatchingChecksumError when checksum is None
Hi @jxmorris12, we have discovered the bug why `None` checksums wrongly appeared when generating the `dataset_infos.json` file:
- #3892

The fix will be accessible once this PR merged. And we are planning to do our 2.0 release today.

We are also working on updating all our docs for our release today.
I ran into the following error when adding a new dataset:

```bash
expected_checksums = {'https://adversarialglue.github.io/dataset/dev.zip': {'checksum': None, 'num_bytes': 40662}}
recorded_checksums = {'https://adversarialglue.github.io/dataset/dev.zip': {'checksum': 'efb4cbd3aa4a87bfaffc310ae951981cc0a36c6c71c6425dd74e5b55f2f325c9', 'num_bytes': 40662}}
verification_name = 'dataset source files'

    def verify_checksums(expected_checksums: Optional[dict], recorded_checksums: dict, verification_name=None):
        if expected_checksums is None:
            logger.info("Unable to verify checksums.")
            return
        if len(set(expected_checksums) - set(recorded_checksums)) > 0:
            raise ExpectedMoreDownloadedFiles(str(set(expected_checksums) - set(recorded_checksums)))
        if len(set(recorded_checksums) - set(expected_checksums)) > 0:
            raise UnexpectedDownloadedFile(str(set(recorded_checksums) - set(expected_checksums)))
        bad_urls = [url for url in expected_checksums if expected_checksums[url] != recorded_checksums[url]]
        for_verification_name = " for " + verification_name if verification_name is not None else ""
        if len(bad_urls) > 0:
            error_msg = "Checksums didn't match" + for_verification_name + ":\n"
>           raise NonMatchingChecksumError(error_msg + str(bad_urls))
E           datasets.utils.info_utils.NonMatchingChecksumError: Checksums didn't match for dataset source files:
E           ['https://adversarialglue.github.io/dataset/dev.zip']

src/datasets/utils/info_utils.py:40: NonMatchingChecksumError
```

## Expected results
The dataset downloads correctly, and there is no error.

## Actual results
Datasets library is looking for a checksum of None, and it gets a non-None checksum, and throws an error. This is clearly a bug.
NonMatchingChecksumError when checksum is None 
 I ran into the following error when adding a new dataset:

```bash
expected_checksums = {'https://adversarialglue.github.io/dataset/dev.zip': {'checksum': None, 'num_bytes': 40662}}
recorded_checksums = {'https://adversarialglue.github.io/dataset/dev.zip': {'checksum': 'efb4cbd3aa4a87bfaffc310ae951981cc0a36c6c71c6425dd74e5b55f2f325c9', 'num_bytes': 40662}}
verification_name = 'dataset source files'

    def verify_checksums(expected_checksums: Optional[dict], recorded_checksums: dict, verification_name=None):
        if expected_checksums is None:
            logger.info("Unable to verify checksums.")
            return
        if len(set(expected_checksums) - set(recorded_checksums)) > 0:
            raise ExpectedMoreDownloadedFiles(str(set(expected_checksums) - set(recorded_checksums)))
        if len(set(recorded_checksums) - set(expected_checksums)) > 0:
            raise UnexpectedDownloadedFile(str(set(recorded_checksums) - set(expected_checksums)))
        bad_urls = [url for url in expected_checksums if expected_checksums[url] != recorded_checksums[url]]
        for_verification_name = " for " + verification_name if verification_name is not None else ""
        if len(bad_urls) > 0:
            error_msg = "Checksums didn't match" + for_verification_name + ":\n"
>           raise NonMatchingChecksumError(error_msg + str(bad_urls))
E           datasets.utils.info_utils.NonMatchingChecksumError: Checksums didn't match for dataset source files:
E           ['https://adversarialglue.github.io/dataset/dev.zip']

src/datasets/utils/info_utils.py:40: NonMatchingChecksumError
```

## Expected results
The dataset downloads correctly, and there is no error.

## Actual results
Datasets library is looking for a checksum of None, and it gets a non-None checksum, and throws an error. This is clearly a bug. 
 Hi @jxmorris12, we have discovered the bug why `None` checksums wrongly appeared when generating the `dataset_infos.json` file:
- #3892

The fix will be accessible once this PR merged. And we are planning to do our 2.0 release today.

We are also working on updating all our docs for our release today.