agent: Update thread label to use plural form (#27971)

Update thread label to match the other contexts.

|Before|After|
|--|--|

|![image](https://github.com/user-attachments/assets/6e02808e-50d7-480f-a9ca-251e9519a71d)|![image](https://github.com/user-attachments/assets/174aad84-9e55-4531-bb4a-1a1adaa46418)|

Release Notes:

- N/A
b4af5b2ce05brian committed on 4/2/2025, 10:33:05 PM· committed by GitHubparentee33d31
1 file changedLine totals unavailable