Fix T68317: Panel "A" key doesn't collapse subpanels properly

We need to only collapse or expand the first panel under the cursor
rather than all of them. Note that whether the parent panel or
the subpanel is first depends on the order of the uiBlocks in the
region's list.

source/blender/editors/interface/interface_panel.c

@@ -2410,7 +2410,7 @@ int ui_handler_panel_region(bContext *C,
       if (event->type == EVT_AKEY && !IS_EVENT_MOD(event, shift, ctrl, alt, oskey)) {
         retval = WM_UI_HANDLER_BREAK;
         ui_handle_panel_header(C, block, mx, event->type, event->ctrl, event->shift);
-        continue;
+        break;
       }
     }