Use inline onload event instead of jQuery load

[kvnang]

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• 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:

Fixes issue on WooCommerce 6.1.0, related to #31407, as using jQuery .load() function triggers error and breaking flexslider gallery. Using inline onload event will achieve the expected output.

How to test the changes in this Pull Request:

(Referenced from #31407)

1. In the single product page with more than one image, inspect the flexbox nav
2. The image thumbnail will be like this: <img onload="this.width = this.naturalWidth; this.height = this.naturalHeight" src="t-shirt-100x100.jpg" draggable="false" width="100" height="100" alt="t-shirt"> (before was <img src="t-shirt-100x100.jpg" draggable="false">)

Changelog entry

Enter a summary of all changes on this Pull Request. This will appear in the changelog if accepted.

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.

[Mte90]

@jeffstieler can you look on this for the next minor?

[jeffstieler]

Works as intended (w/o jQuery migrate) - thank you for the fix!

[github-actions]

Hi @claudiosanches, thanks for merging this pull request. Please take a look at these follow-up tasks you may need to perform:

• Add the status: needs changelog label
• Add the status: needs testing instructions label