[omnibox][history-embeddings] Decrease top-padding by 8px

https://screenshot.googleplex.com/BUQAcfbbkawGjMF

Decreases padding between "summary" header and the answer.

Only affects the answer state; doesn't affect the loading or error
states. The error state already had the smaller padding, so this change
improves consistency.

Bug: 378151813
Low-Coverage-Reason: HARD_TO_TEST Omnibox UI
Change-Id: I27b5766992f05f51df1b0475bffd64e930be85cb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6014182
Auto-Submit: manuk hovanesian <manukh@chromium.org>
Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
Commit-Queue: manuk hovanesian <manukh@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1382607}