[Bug]: groupProductsForBatchStep does not allow for product variant updates when a product is being updated

[fogine]

Package.json file

{
  "name": "medusa-starter-default",
  "version": "0.0.1",
  "description": "A starter for Medusa projects.",
  "author": "Medusa (https://medusajs.com)",
  "license": "MIT",
  "keywords": [
    "sqlite",
    "postgres",
    "typescript",
    "ecommerce",
    "headless",
    "medusa"
  ],
  "scripts": {
    "build": "medusa build",
    "seed": "medusa exec ./src/scripts/seed.ts",
    "start": "medusa start",
    "dev": "medusa develop",
    "test:integration:http": "TEST_TYPE=integration:http NODE_OPTIONS=--experimental-vm-modules jest --silent=false --runInBand --forceExit",
    "test:integration:modules": "TEST_TYPE=integration:modules NODE_OPTIONS=--experimental-vm-modules jest --silent --runInBand --forceExit",
    "test:unit": "TEST_TYPE=unit NODE_OPTIONS=--experimental-vm-modules jest --silent --runInBand --forceExit"
  },
  "dependencies": {
    "@medusajs/admin-sdk": "2.1.3",
    "@medusajs/cli": "2.1.3",
    "@medusajs/framework": "2.1.3",
    "@medusajs/medusa": "2.1.3",
    "@mikro-orm/core": "5.9.7",
    "@mikro-orm/knex": "5.9.7",
    "@mikro-orm/migrations": "5.9.7",
    "@mikro-orm/postgresql": "5.9.7",
    "awilix": "^8.0.1",
    "axios": "^1.7.9",
    "pg": "^8.13.0",
    "printify-sdk-js": "^1.2.0-beta",
    "rambda": "^9.4.1"
  },
  "devDependencies": {
    "@medusajs/test-utils": "2.1.3",
    "@mikro-orm/cli": "5.9.7",
    "@swc/core": "1.5.7",
    "@swc/jest": "^0.2.36",
    "@types/jest": "^29.5.13",
    "@types/node": "^20.0.0",
    "@types/react": "^18.3.2",
    "@types/react-dom": "^18.2.25",
    "jest": "^29.7.0",
    "prop-types": "^15.8.1",
    "react": "^18.2.0",
    "react-dom": "^18.2.0",
    "ts-node": "^10.9.2",
    "typescript": "^5.6.2",
    "vite": "^5.2.11"
  },
  "engines": {
    "node": ">=20"
  }
}

Node.js version

20.18.1

Database and its version

16.2

Operating system name and version

linux

Browser name

No response

What happended?

When I provide a product:AdminCreateProduct & {id?: string} with id and variants to the groupProductsForBatchStep it always trying to create new product variants which will fail if a variant with the same SKU already exists.
Currently it does not allow for the variant to be updated (no variant id can be provided).

Expected behavior

Should be possible to provide variant id in which case it should update the product variant instead of dong insert

Actual behavior

its trying to create product variant duplicate

Link to reproduction repo

its more of a design issue