Fix `TabBar` size when theme changes

(cherry picked from commit fdba051a40c36bb1528a2aaf840531f19ffa8615)

scene/gui/tab_bar.cpp

@@ -373,6 +373,7 @@ void TabBar::_notification(int p_what) {
 			}
 
 			queue_redraw();
+			update_minimum_size();
 
 			[[fallthrough]];
 		}