[FIX] mrp : Confirm MO twice generates multiple stock move

Issue: When two Odoo webpage are open on a Manufacturing order, it is
possible to mark the MO as todo twice, then when trying to record the
production, there will be a traceback Expected Singleton

Steps to reproduce:
 1) Install MRP
 2) Create a Manufacturing order for a Product with a BO
 3) Save, open a new odoo webclient and go to the same MO
 4) Mark as todo on each webclient
 5) Check availability on each webclient
 6) Produce on each webclient, and save the wizard
 -> Traceback Expected Singleton

opw-2636556

closes odoo/odoo#76210

Signed-off-by: Arnold Moyaux <amoyaux@users.noreply.github.com>

addons/mrp/models/mrp_production.py

@@ -686,6 +686,9 @@ class MrpProduction(models.Model):
     def action_confirm(self):
         self._check_company()
         for production in self:
+            # Avoid confirming it twice
+            if production.state != 'draft':
+                continue
             if not production.move_raw_ids:
                 raise UserError(_("Add some materials to consume before marking this MO as to do."))
             for move_raw in production.move_raw_ids:

addons/mrp/tests/test_workorder_operation.py

@@ -1552,3 +1552,39 @@ class TestRoutingAndKits(SavepointCase):
         wo2.button_start()
         self.assertEqual(wo2.qty_producing, 10)
         self.assertEqual(wo2.finished_lot_id, lot1)
+
+    def test_confirm_twice(self):
+        """
+        Test that when confirming a production twice (mark as to do), the moves are only generated once
+        One assert and one "assertNotRaise"
+        """
+        product_inside = self.env['product.product'].create({'name': 'Wood'})
+        product = self.env['product.product'].create({'name': 'Woooden stick'})
+        bom = self.env['mrp.bom'].create({
+            'product_id': product.id,
+            'product_tmpl_id': product.product_tmpl_id.id,
+            'product_qty': 1.0,
+            'type': 'normal',
+            'bom_line_ids': [(0, 0, {'product_id': product_inside.id, 'product_qty': 1})]
+        })
+
+        production_table_form = Form(self.env['mrp.production'])
+        production_table_form.product_id = product
+        production_table_form.bom_id = bom
+        production_table_form.product_qty = 2.0
+        production_table = production_table_form.save()
+        # Confirm twice to generate the issue
+        production_table.action_confirm()
+        previous_move_finished_ids = production_table.move_finished_ids
+        production_table.action_confirm()
+        # The actual test
+        self.assertEqual(production_table.move_finished_ids, previous_move_finished_ids, "Confirming it twice should not generate another move finished id")
+        # Then we continue testing the business flow for double protection
+        # since there is a blocking traceback we want to ensure it doesn't appear
+        production_table.action_assign()
+        context = {'active_id': production_table.id, 'active_model': 'mrp.production'}
+        wizard = self.env['mrp.product.produce'].with_context(context).create({})
+
+        # Will raise Expected Singleton if we actually managed to confirm twice
+        wizard.do_produce()
+