[FIX] sale: Sale channels duplicate field

Steps to reproduce the bug:

- In CRM, create an new Sales Channel
- Go to Reporting/Sales Channels
- Click in the new channel on "Click to define a target"

Bug:

Two input fields called "Set an invoicing target" appeared in the new channel

opw:1889406

closes odoo/odoo#27781

addons/sale/static/src/js/sale.js

@@ -21,8 +21,8 @@ KanbanRecord.include({
         ev.preventDefault();
 
         this.$target_input = $('<input>');
-        this.$('.o_kanban_primary_bottom').html(this.$target_input);
-        this.$('.o_kanban_primary_bottom').prepend(_t("Set an invoicing target: "));
+        this.$('.o_kanban_primary_bottom:last').html(this.$target_input);
+        this.$('.o_kanban_primary_bottom:last').prepend(_t("Set an invoicing target: "));
         this.$target_input.focus();
 
         var self = this;