Fix chat icon in light theme (microsoft#186797)

Author: roblourens

src/vs/workbench/contrib/chat/browser/media/chatEditor.css

@@ -3,6 +3,7 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
+.vs .show-file-icons .chat-editor-label.file-icon::before,
 .show-file-icons .chat-editor-label.file-icon::before {
 	content: '\EAC7';
 	font-family: 'codicon';