Ford: block stock ACC warnings on OP long (#28185)

Override this signal which the stock system uses to show messages such
as "ACC unavailable", "Speed too low" and causes the canceled sound to
play.

selfdrive/car/ford/fordcan.py

@@ -187,9 +187,11 @@ def create_acc_ui_msg(packer, CP, main_on: bool, enabled: bool, standstill: bool
   if CP.openpilotLongitudinalControl:
     values.update({
       "AccStopStat_D_Dsply": 2 if standstill else 0,              # Stopping status text
+      "AccMsgTxt_D2_Rq": 0,                                       # ACC text
       "AccTGap_B_Dsply": 0,                                       # Show time gap control UI
       "AccFllwMde_B_Dsply": 1 if hud_control.leadVisible else 0,  # Lead indicator
       "AccStopMde_B_Dsply": 1 if standstill else 0,
+      "AccWarn_D_Dsply": 0,                                       # ACC warning
       "AccTGap_D_Dsply": 4,                                       # Fixed time gap in UI
     })