Close the menu on keypress.

After _InvokeItem(), call QuitTracking() to close the menu.
Incidentally this also seems to fix #9863.

src/kits/interface/Menu.cpp

@@ -584,6 +584,7 @@ BMenu::KeyDown(const char* bytes, int32 numBytes)
 					continue;
 
 				_InvokeItem(item);
+				_QuitTracking(false);
 				break;
 			}
 			break;