Fix item height in wiki sidebar

What does this MR do and why?

this MR is to add height of item in wiki sidebar that should have been done in !112997 (merged) so that the add child button will not overflow the line when being hovered

related design: #383524 (comment 1303364702)

Screenshots or screen recordings

before	after

How to set up and validate locally

1.visit wiki page in project, and check the change

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

/cc @daveliu @JeremyWuuuuu