Can't retrieve boot log due to 'RetrieveBootDiagnosticsDataResult' object has no attribute 'done'

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

## Describe the bug

**Command Name**
`az vm boot-diagnostics get-boot-log`

**Errors:**
```
'RetrieveBootDiagnosticsDataResult' object has no attribute 'done'
Traceback (most recent call last):
python3.6/site-packages/knack/cli.py, ln 233, in invoke
cmd_result = self.invocation.execute(args)
cli/core/commands/__init__.py, ln 660, in execute
raise ex
cli/core/commands/__init__.py, ln 723, in _run_jobs_serially
results.append(self._run_job(expanded_arg, cmd_copy))
cli/core/commands/__init__.py, ln 716, in _run_job
six.reraise(*sys.exc_info())
lib/python3.6/site-packages/six.py, ln 703, in reraise
raise value
...
azure/cli/core/__init__.py, ln 808, in default_command_handler
return op(**command_args)
cli/command_modules/vm/custom.py, ln 1501, in get_boot_log
uris = LongRunningOperation(cmd.cli_ctx)(poller)
cli/core/commands/__init__.py, ln 958, in __call__
while not poller.done():
AttributeError: 'RetrieveBootDiagnosticsDataResult' object has no attribute 'done'
```

## 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 vm boot-diagnostics get-boot-log -g {} -n {}`

## Expected Behavior

## Environment Summary
```
Linux-5.11.0-27-generic-x86_64-with-debian-bullseye-sid
Python 3.6.10
Installer: DEB

azure-cli 2.20.0 *

```
## Additional Context