docs(adk): fix run_async example and correct ticketId payload key

Merge #3875

# Problem
The example in `contributing/samples/human_in_loop/README.md` shows:

```python
await runner.run_async(...)
```

However, `run_async` returns an **async generator**, so awaiting it raises:

```
TypeError: object async_generator can't be used in 'await' expression
```

Additionally, the example payload uses `"ticket-id"` while ADK tools and other examples use `"ticketId"`, creating a mismatch that breaks copy/paste usage.

# Solution
- Updated the snippet to consume the async generator correctly:

```python
async for event in runner.run_async(...):
    ...
```

- Aligned the payload key from `"ticket-id"` → `"ticketId"` for consistency with ADK schema and other examples.

These changes make the example runnable and consistent with the API’s actual behavior.

# Testing Plan
This PR is a **small documentation correction**, so no unit tests are required per contribution guidelines.

- Verified the corrected snippet manually to ensure it no longer raises `TypeError`.

# Checklist
- [x] I have read the CONTRIBUTING.md document.
- [x] I have performed a self-review of my own code.
- [ ] I have commented my code, particularly in hard-to-understand areas. *(N/A – docs only)*
- [ ] I have added tests that prove my fix is effective or that my feature works. *(N/A – docs only)*
- [ ] New and existing unit tests pass locally with my changes. *(N/A – docs only)*
- [x] I have manually tested my changes end-to-end.
- [ ] Any dependent changes have been merged and published in downstream modules. *(N/A)*

COPYBARA_INTEGRATE_REVIEW=#3875 from krishna-dhulipalla:docs/fix-adk-run_async-example 83fc5b4
PiperOrigin-RevId: 842952362

Author: krishna-dhulipalla

contributing/samples/human_in_loop/README.md

@@ -18,7 +18,7 @@ This example demonstrates an agent using a long-running tool (`ask_for_approval`
     # Example: After external approval
     updated_tool_output_data = {
         "status": "approved",
-        "ticket-id": ticket_id, # from original call
+        "ticketId": ticket_id, # from original call
         # ... other relevant updated data
     }
 
@@ -31,12 +31,13 @@ This example demonstrates an agent using a long-running tool (`ask_for_approval`
     )
 
     # Send this back to the agent
-    await runner.run_async(
+    async for _ in runner.run_async(
         # ... session_id, user_id ...
         new_message=types.Content(
             parts=[updated_function_response_part], role="user"
         ),
-    )
+    ):
+        pass  # exhaust generator (or handle events)
     ```
 6.  **Agent Acts on Update**: The agent receives this message containing the `types.FunctionResponse` and, based on its instructions, proceeds with the next steps (e.g., calling another tool like `reimburse`).