Add back vertical scrollbar in console sidebar

A previous CL (https://crrev.com/c/5830446) accidentally
removed the vertical scrollbar of the console sidebar.
This re-adds the corresponding css to show it.

Before: https://i.imgur.com/mISRG0z.png
After: https://i.imgur.com/ogqi3uP.png
Fixed: 386610911
Change-Id: I34c6edf4be4da3699e60653cf2194ae40924eb95
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/6148233
Auto-Submit: Kim-Anh Tran <[email protected]>
Reviewed-by: Benedikt Meurer <[email protected]>
Commit-Queue: Benedikt Meurer <[email protected]>

Author: ktran

front_end/panels/console/consoleSidebar.css

@@ -4,6 +4,10 @@
  * found in the LICENSE file.
  */
 
+:host {
+  overflow: auto;
+}
+
 .count {
   flex: none;
   margin: 0 var(--sys-size-3);