Prevent user to modify clearing reconciled field on payment

Closes #12454

modules/account_payment_clearing/payment.py

@@ -139,7 +139,7 @@ class Payment(metaclass=PoolMeta):
     clearing_move = fields.Many2One('account.move', 'Clearing Move',
         readonly=True)
     clearing_reconciled = fields.Boolean(
-        "Clearing Reconciled",
+        "Clearing Reconciled", readonly=True,
         states={
             'invisible': ~Eval('clearing_move'),
             },