Fix button height bug with in menus

When `.button` is not a direct descendant of `.menu` (for example, when it is wrapped), it would not get this style applied, which caused inconsistent heights of buttons that were wrapped vs. ones that weren't. Removed the `>` operator to fix this.

Refs:

- go-gitea/gitea#3091
- https://try.gitea.io/silverwind/testcopy/commits/branch/master

src/definitions/collections/menu.less

@@ -140,7 +140,7 @@
      Button
 ---------------*/
 
-.ui.menu:not(.vertical) .item > .button {
+.ui.menu:not(.vertical) .item .button {
   position: relative;
   top: @buttonOffset;
   margin: @buttonMargin;