UI: Style tweaks to issue selection (#6196)

- Prevent jump in layout when selecting the first issue
- Remove useless padding on top of first issue

public/less/_repository.less

@@ -1583,6 +1583,10 @@
     display: none;
 }
 
+#issue-actions {
+  margin-top: -1rem !important; // counteract padding from Semantic
+}
+
 #issue-actions.hide {
     display: none;
 }
@@ -1593,7 +1597,6 @@
 
 .issue.list {
     list-style: none;
-    padding-top: 15px;
     >.item {
         padding-top: 15px;
         padding-bottom: 10px;