Fix docs build for Milvus Async API notebook

[jaelgu]

Description

Fix doc build issue to show MilvusAsyncAPIDemo notebook in side menu.

Type of Change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• This change requires a documentation update

How Has This Been Tested?

Your pull-request will likely not be merged unless it is covered by some form of impactful unit testing.

• I believe this change is already covered by existing unit tests

Suggested Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I ran make format; make lint to appease the lint gods

[logan-markewich]

Fyi normally when I do a "stable" release on the repo, I run a script that auto-populates this. But totally fine to manually add it too