Updated error message text when notebook size exceeds 10485760 bytes

[lcirvin]

When attempting to download a notebook greater than 10485760 bytes in size, the API previously returned an error formatted as follows:

{"error_code": "BAD_REQUEST", "message": "Size exceeds 10485760 bytes", "http_status_code": 400, "path": "/Users/[email protected]/xxx"}

There appears to have been an update, such that the error is now formatted more along the lines of:

{"error_code": "BAD_REQUEST", "message": "Notebook size exceeded limit: *(some file size)* > 10485760", "http_status_code": 400, "path": "/Users/[email protected]/xxx"}

This PR updates WorkspaceClient.py to account for the update, to restore functionality provided by the --skip-large-nb flag

[CLAassistant]

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