Add is_string check to safeguard against array meta keys.

[thijsoo]

Context

• It seems there are scenario's where deleted_post_meta is called with an array as the meta_keys parameter. We want to safeguard our code, since that gives a fatal in php 8.1

Summary

This PR can be summarized in the following changelog entry:

• Fixes a bug where there would be a fatal error when deleting post meta in PHP 8.1 and higher. Props to @izzygld.

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:

• Make sure you are on php 8.1 or higher.
• Add the following code to your functions.php or a mu plugin.

add_action( 'admin_init', 'admin_init_cb', 1 );
function admin_init_cb() {
	do_action( 'deleted_post_meta', 1, null, ['this','is','an','array'] );
}

• Without this PR/RC make sure you get an fatal error.
• With this pr make sure this error is gone.

Relevant test scenarios

• Changes should be tested with the browser console open
• Changes should be tested on different posts/pages/taxonomies/custom post types/custom taxonomies
• Changes should be tested on different editors (Default Block/Gutenberg/Classic/Elementor/other)
• Changes should be tested on different browsers
• Changes should be tested on multisite

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:

Impact check

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

• This touches the way we handle post meta. So it would be good to smoke test setting some values in the sidebare/metabox. Like the focus keyphrase.

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], added test instructions for Shopify and attached the Shopify label to this PR.

Documentation

• I have written documentation for this change. For example, comments in the Relevant technical choices, comments in the code, documentation on Confluence / shared Google Drive / Yoast developer portal, or other.

Quality assurance

• I have tested this code to the best of my abilities.
• During testing, I had activated all plugins that Yoast SEO provides integrations for.
• I have added unit tests 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.
• I have written this PR in accordance with my team's definition of done.
• I have checked that the base branch is correctly set.

Innovation

• No innovation project is applicable for this PR.
• This PR falls under an innovation project. I have attached the innovation label.
• I have added my hours to the WBSO document.

Fixes #

[coveralls]

Pull Request Test Coverage Report for Build d5fd5b1fd0efa138d72835d9c6467dcb2fdfdf29

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 52.566%

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Totals
Change from base Build dfcc56dd8ea44984b27442be5b9197f6659ad9d9:	0.0%
Covered Lines:	28352
Relevant Lines:	54400

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💛 - Coveralls

[pls78]

CR && Acc: ✅

[izzygld]

@thijsoo Was this pushed into the latest release (22.5)?

Fixes a bug where there would be a fatal error when deleting post meta in PHP 8.1 and higher. Props to @izzygld.

I don't see any mention of it on the release notes?

[thijsoo]

@izzygld This will be included in 22.6. So you should see it mentioned there in the release notes :) You can see the tentative tag here: https://github.com/Yoast/wordpress-seo/releases/tag/22.6-RC1