[CrOS settings] Fix issue where menu items do not have space between

Fix regression caused by this cl crrev.com/c/2490785.

screenshot: https://screenshot.googleplex.com/5nHRPBM6j8Wkn9H.png

Bug: 1148721
Change-Id: I6070847c567f0ccee28a574722996445597c3d3f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2541226
Commit-Queue: Nnamdi Theodore Johnson-kanu <tjohnsonkanu@google.com>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827968}

chrome/browser/resources/settings/chromeos/os_settings_menu/os_settings_menu.html

@@ -63,6 +63,7 @@
         color: var(--menu-text-color);
         display: flex;
         font-weight: 500;
+        margin-bottom: 8px;
         margin-inline-end: 2px;
         min-height: 32px;
         padding-inline-start: 20px;