Fix style for notices (#24636)

* Fix style for notices

* Fix snapshots

* Address feedback

* Update snapshots

webapp/channels/src/sass/components/_system-notice.scss

@@ -45,7 +45,7 @@
 
 .system-notice__body {
     padding: 0 0 16px 16px;
-    line-height: 16px;
+    line-height: 20px;
 }
 
 .system-notice__footer {