Panels: fix positioning of the header title (#29167)

the menu toggle icon is now absolute positioned and it no longer  affects the centering of the menu title

public/sass/components/_panel_header.scss

@@ -60,6 +60,8 @@ $panel-header-no-title-zindex: 1;
 }
 
 .panel-menu-toggle {
+  position: absolute;
+  top: calc(50% - 9px);
   color: $text-color-weak;
   cursor: pointer;
   margin: 2px 0 0 2px;