[FIX] mrp: display the BoM overview of the current product variant

Stpes to reproduce the bug:
- Create a storable product “P1” with 2 variants:
    - Color: Red and blue in this order
    - Create a BoM for each variant
- Create a SO:
    - select the product “P1 - blue” → the second variant
    - Click on the forecast button →  manufacturing forecast

Problem:
The BoM overview is showing the wrong product variation because it pulls
the default BoM of the base product (always the first variant from the
list)

opw-3166074

closes odoo/odoo#115421

X-original-commit: 873d6d921c3955b707d10826a898ae405f296531
Signed-off-by: Djamel Touati (otd) <otd@odoo.com>

addons/mrp/static/src/mrp_forecasted/forecasted_buttons.js

@@ -8,8 +8,8 @@ patch(ForecastedButtons.prototype, 'mrp.ForecastedButtons',{
     setup() {
         this._super.apply();
         onWillStart(async () =>{
-            const res = await this.orm.call(this.resModel, 'read', [this.productId], {fields: ['bom_ids']});
-            this.bomId = res[0].bom_ids && res[0].bom_ids[0];
+            const res = (await this.orm.call(this.resModel, 'read', [this.productId], {fields: ['bom_ids', 'variant_bom_ids']}))[0];
+            this.bomId = res.variant_bom_ids[0] || res.bom_ids[0];
         });
     },