Unable to list notebooks

### **This is autogenerated. Please review and update as needed.**

## Describe the bug
When trying to list notebooks via CLI, I get the error described below. I also have an open Azure support ticket addressing similar behavior in the portal where my notebook went missing and seems to timeout when trying to locate notebooks (just a theory)

**Command Name**
`az synapse notebook list`

**Errors:**
```
Unable to deserialize to object: type, AttributeError: 'str' object has no attribute 'get'
Traceback (most recent call last):
python3.8/site-packages/msrest/serialization.py, ln 1416, in _deserialize
found_value = key_extractor(attr, attr_desc, data)
python3.8/site-packages/msrest/serialization.py, ln 1160, in rest_key_extractor
return working_data.get(key)
AttributeError: 'str' object has no attribute 'get'

...

python3.8/site-packages/msrest/serialization.py, ln 1160, in rest_key_extractor
return working_data.get(key)
msrest.exceptions.DeserializationError: Unable to deserialize to object: type, AttributeError: 'str' object has no attribute 'get'
```

## To Reproduce:
Steps to reproduce the behavior. Note that argument values have been redacted, as they may contain sensitive information.

- _Put any pre-requisite steps here..._
`az synapse notebook list --workspace-name {MY_WORKSPACE_NAME}`

## Expected Behavior
I should see a list of notebooks

## Environment Summary
```
macOS-11.2.1-x86_64-i386-64bit
Python 3.8.7
Installer: HOMEBREW

azure-cli 2.17.1 *

Extensions:
databricks 0.7.0
azure-devops 0.18.0

```
## Additional Context

Inizia dal punto di ingresso dell’elenco di az synapse notebook e riproduci il comando con un nome di workspace. Confronta i dati dei notebook restituiti con il traceback di deserializzazione di msrest, quindi verifica che un output riuscito elenchi i notebook senza AttributeError. Il payload non indica alcun file sorgente né alcun test, quindi individuare l’implementazione e aggiungere la coverage richiederà una ricerca nel repository.

Scritto dal modello di indicizzazione a partire dal testo della issue.