[LiveValidation RPaaS] Address `git prune` error

Jobs are failing with

```
Validator: unable to refresh the Validator. Error:Error: error: cannot lock ref 'refs/remotes/origin/test/privatelinksdk': 'refs/remotes/origin/test' exists; cannot create 'refs/remotes/origin/test/privatelinksdk'
From[ https://github.com/Azure/azure-rest-api-specs](https://github.com/Azure/azure-rest-api-specs)
! [new branch] test/privatelinksdk -> origin/test/privatelinksdk (unable to update local ref)
error: some local refs could not be updated; try running
'git remote prune origin' to remove any old, conflicting branches
```

Anything we can do if we see this error?