Fix WebP handling when editing images based on WordPress 6.3 change

[felixarntz]

Summary

Unit tests currently fail in trunk, based on the 6.3 release from yesterday. There are two problems that lead to those failures:

• WordPress 6.3 makes the Fetchpriority module useless. The module is already not being loaded with that version, so we need to ensure we don't run tests in that case either.
• WordPress 6.3 actually comes with a breaking change in a low-level function which we use in the WebP Uploads module: Per https://core.trac.wordpress.org/ticket/57685 / https://core.trac.wordpress.org/changeset/55935, editing thumbnails (or all image sizes other than thumbnails) is no longer enabled by default, which is technically a breaking change 😞

This PR brings parity with those changes:

• Handle the image editing target values thumbnail and nothumb only when editing thumbnails separately is enabled (if using WP 6.3 or greater, per the new filter).
• Skip tests that aren't relevant based on the related new WP 6.3 functionality.

Checklist

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[felixarntz]

@joemcgill Turns out there is a breaking change in WordPress 6.3 😞

Not sure if it's worth fixing since it's a very low-level function, but in any case I opened https://core.trac.wordpress.org/ticket/59040 for consideration.

[mukeshpanchal27]

Thanks @felixarntz for the PR. Left one question.

With the changes we have to update WebP Uploads plugin.

[felixarntz]

@mukeshpanchal27

With the changes we have to update WebP Uploads plugin.

Good catch! I've prepared the WebP Uploads standalone plugin for the update in 65b5fdc.

[mukeshpanchal27]

Thanks @felixarntz for the changes. LGTM!

[mukeshpanchal27]

@joemcgill Could you please take a look so we can merge this PR. Thanks!

[joemcgill]

The updates look good to me. I've not gotten a chance to review the breaking change in WP yet, but thanks for reporting it.