[unified-consent] Fix bottom spacing of passphrase Save button

Screenshot before:
https://drive.google.com/file/d/1docQTG83IMfNalyaJn8VOZ_bWIbMFq0J/view?usp=sharing
Screenshot after:
https://drive.google.com/file/d/1u6gCMPVEqsLy9fkuxhqGlrqpBYQzSmj_/view?usp=sharing

Bug: 861649
Change-Id: Iecef069e5fe5007711c0b8b7191e9c3534c367f6
Reviewed-on: https://chromium-review.googlesource.com/1186723
Commit-Queue: Thomas Tangl <tangltom@chromium.org>
Reviewed-by: Scott Chen <scottchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585780}

chrome/browser/resources/settings/people_page/sync_page.html

@@ -34,6 +34,10 @@
         margin-inline-start: var(--settings-indent-width);
       }
 
+      #create-password-box {
+        margin-bottom: 1em;
+      }
+
       #create-password-box .list-item {
         margin-bottom: var(--cr-form-field-bottom-spacing);
       }