This pull request aims at fixing [https://github.com//issues/38243](this issue).
It fixes the synchronisation of a website scoped attribute in a multi store environment.

Description (*)

I fixed the issue by applying another condition in the _updateAttribute method of the Magento\Catalog\Model\ResourceModel\AbstractResource class.

A fix made recently on this method brought the bug. This method used to only call the _saveAttributeValue method of that same class. Now it has its own logic is the updated attribute is not new. I added a condition that the updated attribute must not be website scoped in a multi store environment.

I did not want to add too much code since the modificatoins that were made on this method took place for a specific reason that i do not know.

Fixed Issues (if relevant)

1. Fixes _updateAttribute function started to behave incorrectly when trying to update an attribute which is on a website scope. #38243

Manual testing scenarios (*)

1. Create 3 stores, each one of then will have their own store view.
2. Create a Yes/No attribute with the website scope.
3. Add this attribute to the default attribute set
4. Create a simple product, set this Yes/No attribute to false on the scope of a store view.
5. In a custom script :

$product = $this->productRepository->get('some-product-sku', false, 1);
$product->addAttributeUpdate('show_discount', 1, $product->getStoreId());

Adapt the sku and the store id to you use case.

6. Check in the DB, the attribute should have the value "1" for all stores. If not, my fix does not work.

Questions or comments

It doesn't seem i could write an automated test for this use case. Do you confirm ?
I took time to choose the right approach. I could not rollback the changes that were made on the issue at the origin of this bug even though the code written did not take into account the scope of the attribute.
So i decided to treat only the very issue I was working on. I had to make so that previous work would still be present and this issue would be fixed.

I hope you agree with that approach.

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• README.md files for modified modules are updated and included in the pull request if any README.md predefined sections require an update
• All automated tests passed successfully (all builds are green)