Stale key name in automatic tracing changelog entry

### Example URL(s)

https://developers.cloudflare.com/changelog/post/2025-11-07-automatic-tracing/

### Actual Behavior

The changelog post at [/changelog/post/2025-11-07-automatic-tracing/](https://developers.cloudflare.com/changelog/post/2025-11-07-automatic-tracing/) shows `observability.tracing` (the beta key name), but the key was renamed to `observability.traces` before GA.

The current docs at [/workers/observability/traces/](https://developers.cloudflare.com/workers/observability/traces/) correctly shows traces, but the changelog still references the old name, causing confusion for anyone who finds it via search.

### Expected Behavior

Update the snippet in that changelog entry to use observability.traces

### Additional information

_No response_