Prevent UPDATE_COMMENT from invalidating the cache of child comments (Fix #1509 )

[riccardobl]

Description

The upsertComment mutation currently returns the list of child comments whenever a comment is edited. This behavior causes the Apollo cache to update, resulting in any new comments appearing upon the re-render triggered by the edit form. This PR modifies the UPDATE_COMMENT fragment to exclude the list of child comments, preventing unintended cache updates. #1509

Checklist

Are your changes backwards compatible? Please answer below:
yes

On a scale of 1-10 how well and how have you QA'd this change and any features it might affect? Please answer below:

9. Comments are updated as expected at different levels of depth, as expected editing doesn't cause the child comments to refresh anymore.

For frontend changes: Tested on mobile? Please answer below:

Did you introduce any new environment variables? If so, call them out explicitly here: