Updating rest namespace for product post type to v3

[joelclimbsthings]

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:

Closes #36990 .

How to test the changes in this Pull Request:

1. Checkout branch.
2. Open the network tab in your browser dev tools.
3. Either get the productId of an existing product, or create a new one.
4. In the console, run window.wp.data.select( 'core' ).getEditedEntityRecord( 'postType', 'product', PRODUCT_ID ) with that product ID in place of PRODUCT_ID.
5. Observe that the resulting API request uses the v3 namespace:
   

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 created a changelog file for each project being changed, ie pnpm --filter=<project> changelog add?
• Have you included testing instructions?

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.

[github-actions]

Test Results Summary

Commit SHA: 7da4fae

Test 🧪	Passed ✅	Failed 🚨	Broken 🚧	Skipped ⏭️	Unknown ❔	Total 📊	Duration ⏱️
API Tests	259	0	0	2	0	261	0m 50s
E2E Tests	189	0	0	6	0	195	13m 42s

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To view the full API test report, click here.
To view the full E2E test report, click here.
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[mattsherman]

Verified that v3 of the endpoint is used.