Acceptable values are latest or any semantic version string like 1.9.7. Use this action in workflow to define which version of Istioctl will be used.

- uses: zufardhiyaulhaq/setup-istioctl@v1.0.0
  with:
    version: '<version>'

Refer to the action metadata file for details about all the inputs https://github.com/zufardhiyaulhaq/setup-istioctl/blob/master/.github/workflows/main.yml