Update item type check for workflow actions

[spotakash]

As per SDK, package name correction and item payload correction. Else there will be error indicates event.item is None when you try to access event.item.type. Add a null check before comparing the type

Description

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[Copilot]

Pull request overview

This PR updates the streaming event handling in the azure-ai-projects multi-agent workflow sample to avoid errors when event.item is missing, and adjusts the item type check logic.

Changes:

• Adds a null check for event.item before reading event.item.type during streaming.
• Replaces the workflow-action type comparison with a string-based check.
• Updates the imported model symbol list in the sample.

[Copilot]

ItemResource is imported but never used in this sample. This will trigger unused-import linting in many CI configurations. If the intent is to avoid string literals for the item type check, consider importing/using ItemResourceType instead; otherwise remove this import entirely.

Suggested change

ItemResource,

[Copilot]

This condition hard-codes the item type as the string "workflow_action". The SDK already defines this value in ItemResourceType.WORKFLOW_ACTION, which is safer (avoids typos and stays aligned if the constant ever changes). You can keep the new event.item is not None guard, but compare event.item.type against the enum constant instead of a raw string.