[Sources] Avoid tree item heigh bouncing by setting lineheight (#5890)

Author: darkwing

src/components/shared/ManagedTree.css

@@ -16,6 +16,8 @@
   display: grid;
   grid-template-columns: 1fr;
   align-content: start;
+
+  line-height: 1.4em;
 }
 
 .managed-tree .tree button {