Update changelog to include tasks

Author: LucaButBoring

docs/specification/draft/changelog.mdx

@@ -14,6 +14,7 @@ the previous revision, [2025-06-18](/specification/2025-06-18).
 3. Enhance authorization flows with incremental scope consent via `WWW-Authenticate` ([SEP-835](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/835))
 4. Provide guidance on tool names ([SEP-986](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/1603))
 5. Update `ElicitResult` and `EnumSchema` to use a more standards-based approach and support titled, untitled, single-select, and multi-select enums ([SEP-1330](https://github.com/modelcontextprotocol/modelcontextprotocol/issues/1330)).
+6. Add experimental support for [tasks](/specification/draft/basic/utilities/tasks) to enable tracking durable requests with polling and deferred result retrieval ([SEP-1686](https://github.com/modelcontextprotocol/modelcontextprotocol/issues/1686)).
 
 ## Minor changes