All Submissions:

• Have you followed the WooCommerce Contributing guideline?
• Does your code follow the WordPress' coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

In WooCommerce 6.9, a tip was added under the product image thumbnail in the sidebar of the product edit page (see #33660).

Under certain circumstances, this tip can be rendered multiple times.

This is because the add_filter call is incorrectly called from the constructor of the WC_Simple_Product class. This is not a good location to call add_filter because:

1. There is no guarantee that a plugin or even core functionality will not construct multiple WC_Simple_Product instances while rendering the product edit page, and
2. By calling it from the WC_Simple_Product constructor, it doesn't appear for other product types, such as variable products.

I've changed the implementation to work when editing any product type and to only render a single time.

Fixes #34728.

How to test the changes in this Pull Request:

0. Add the following code to a plugin/mu-plugin. It will trigger the issue:

function test_create_product_objects() {
	$product1 = new WC_Product_Simple();
	$product2 = new WC_Product_Simple();
}

add_action( 'admin_init', 'test_create_product_objects' );

1. Go to Products > Add New
2. Observe the tip in the bottom of the product image metabox.
3. Click the new link and ensure it works as expected.
4. Go to Posts > Add New
5. Verify that the tip does not appear in the bottom of the featured image metabox.

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully run tests with your changes locally?
• Have you created a changelog file for each project being changed, ie pnpm changelog add --filter=<project>?

FOR PR REVIEWER ONLY:

• I have reviewed that everything is sanitized/escaped appropriately for any SQL or XSS injection possibilities. I made sure Linting is not ignored or disabled.