Inconsistent processing of invalid configuration value depending on target hosting plan

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

## Describe the bug

**Command Name**
`az functionapp config set`

**Errors:**

When provided with invalid value for `LinuxFxVersion` parameter, command does not fail with error when target hosting plan is Linux Premium.

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

- Create a linux premium function app
- "FUNCTIONS_WORKER_RUNTIME" = "node",
- `linuxFxVersion` not set explicitly
- `az functionapp config set --name {} --resource-group {} --linux-fx-version "node:12"`

## Expected Behavior

Note `node:12` is invalid value for LinuxFxVersion.

When target plan is Linux Consumption, the command will fail with `Operation returned an invalid status code 'Bad Request'` (when running with `--debug`, more verbose error is `{"Code":"BadRequest","Message":"The parameter LinuxFxVersion has an invalid value." ...`).

Expected: When target plan is Linux Premium, the command should fail with the same error.

## Actual Behavior

When target plan is Linux Premium, the command succeeds. After that, actual node.js version will default to `~10`.

## Environment Summary
```
Linux-4.19.121-linuxkit-x86_64-with-debian-10.7
Python 3.6.10
Installer: DEB

azure-cli 2.19.1

```
## Additional Context