Fix structured data blocks deprecation warning

[Djennez]

Context

• Provides a fix for a deprecation message from WordPress 5.8

Summary

This PR can be summarized in the following changelog entry:

• Fixes a bug where a (debug) deprecation message would show in the widget editor on WordPress 5.8 and above.

Relevant technical choices:

Test instructions

Test instructions for the acceptance test before the PR gets merged

This PR can be acceptance tested by following these steps:

• Install and activate Yoast Free on WordPress 5.8 or above.
• Make sure debugging is active (add to wp-config.php: define( 'WP_DEBUG', true ); and define( 'SCRIPT_DEBUG', true );)
• Navigate to Appearance -> Widgets
• Notice the PHP Notice: wp_enqueue_script() ...
• With this PR, that message won't show.

Test instructions for QA when the code is in the RC

• QA should use the same steps as above.

QA can test this PR by following these steps:

• Make sure the FAQ block keeps functioning as expected on posts and pages.

Impact check

This PR affects the following parts of the plugin, which may require extra testing:

UI changes

• This PR changes the UI in the plugin. I have added the 'UI change' label to this PR.

Other environments

• This PR also affects Shopify. I have added a changelog entry starting with [shopify-seo] and I have added test instructions for Shopify.

Documentation

• I have written documentation for this change.

Quality assurance

• I have tested this code to the best of my abilities
• I have added unittests to verify the code works as intended
• If any part of the code is behind a feature flag, my test instructions also cover cases where the feature flag is switched off.

Fixes #17275
Fixes https://yoast.atlassian.net/browse/IM-505

[Djennez]

Tested ✅