UnderlineNav total height should be `48px` instead of `45px`

[broccolinisoup]

Description

Issue is reported on the #primer-react slack channel by @adrianmg - Thanks 🙏🏻

UnderlineNav v2 component's total height is 45px but according to the design and the production it should be 48px.

Attaching the screenshots Adrian posted on the slack channel

Steps to reproduce

1. Go to https://primer.style/react/storybook/iframe.html?args=&id=drafts-components-underlinenav-features--overflow-template&viewMode=story or any other UnderlineNav v2 stories
2. Inspect the component with a dev tool
3. See the total height is 45px

Version

v.35.18.0

Browser

No response