Not known attribute warn for az sig image-version create

## Describe the bug
`az sig image-version create` outputs warning message cited below, while the command itself seems completed successfully.

**Command Name**
`az sig image-version create`

**Warning:**
```
source is not a known attribute of class and will be ignored
```

## To Reproduce:

- Create image source Linux VM, and get it generalized with `az vm generalize`
- Create shared image gallery and image definition with default settings (for Linux)
- `az sig image-version create -g {} --gallery-name {} --gallery-image-definition {} --gallery-image-version {} --virtual-machine {}`

## Expected Behavior
Completed w/o any warnings.

## Environment Summary
Reproduced on Azure CloudShell
```
Linux-5.4.0-1094-azure-x86_64-with-glibc2.35 (Cloud Shell), CBL-Mariner/Linux
Python 3.9.14
Installer: RPM

azure-cli 2.42.0

Extensions:
ai-examples 0.2.5
ml 2.10.0
ssh 1.1.3

Dependencies:
msal 1.20.0
azure-mgmt-resource 21.1.0b1
```

## Additional Context
Tried with different Azure CLI versions (2.40.0 and 2.41.0) with docker image `mcr.microsoft.com/azure-cli:` to find it reproduces with 2.41.0, while it doesn't with 2.40.0.