Re-establish the vertical spacing in the repository commands

The beautify of the repository commands made in Ida9f3efc1
has accidentally removed the vertical spacing between buttons,
making the organisation of all other repository actions
(e.g., GC and the other provided by plugins) attached together
with their titles and with themselves.

Rectify the situation and give the same space the buttons had
in earlier versions of Gerrit by adding a top-margin to `h3`
as well, that are the titles of the other generic buttons.

Bug: Issue 16389
Release-Notes: skip
Change-Id: If6af1dfe9aeaabf4976f86d4938a7adde6aa896d
diff --git a/polygerrit-ui/app/elements/admin/gr-repo-commands/gr-repo-commands.ts b/polygerrit-ui/app/elements/admin/gr-repo-commands/gr-repo-commands.ts
index 93f9159..9867aa5 100644
--- a/polygerrit-ui/app/elements/admin/gr-repo-commands/gr-repo-commands.ts
+++ b/polygerrit-ui/app/elements/admin/gr-repo-commands/gr-repo-commands.ts
@@ -89,7 +89,8 @@
       subpageStyles,
       sharedStyles,
       css`
-        #form h2 {
+        #form h2,
+        h3 {
           margin-top: var(--spacing-xxl);
         }
         p {