scriptType:

     {
            "name": "scriptType", 
            "type": "pickList",
            "label": "Script Type",
            "defaultValue": "",
            "required": true,
            "helpMarkDown": "Type of script: PowerShell/PowerShell Core/Bat/Shell script. Select Shell/PowerShell Core script when running on Linux agent or Batch/PowerShell/PowerShell Core script when running on Windows agent. PowerShell Core script can run on cross-platform agents (Linux, macOS, or Windows).",
            "options": {
                "ps": "PowerShell",
                "pscore": "PowerShell Core",
                "batch": "Batch",
                "bash": "Shell"
            }
        }

See also

• Azure Pipelines: az pipelines, trigger:, stages:, variables:, parameters:, inputs:, group:, template:, jobs:, job:, steps:, dependsOn:, task:, condition:, resources:, pool:, stage:, extends:, deployment:, scriptType:, inlineScript:, repositories:, pr:, repository:, type:, Default Azure Pipeline, Azure Pipeline Library, Azure Pipeline Job full syntax

https://github.com/microsoft/azure-pipelines-tasks/blob/master/Tasks/AzureCLIV2/task.json