Increase space between non-grouped message bubbles

Co-authored-by: Evan Hahn <69474926+EvanHahn-Signal@users.noreply.github.com>

stylesheets/_modules.scss

@@ -294,8 +294,8 @@
   position: relative;
   display: inline-block;
   border-radius: 18px;
-  margin-bottom: 4px;
-  margin-top: 4px;
+  margin-bottom: 6px;
+  margin-top: 6px;
   min-width: 0px;
   overflow: hidden;