Turn on the Free requirement check

[enricobattocchi]

Context

• Removes the feature flag for the integration introduced in Add an integration to check the Requires Yoast SEO header. #21391

Summary

This PR can be summarized in the following changelog entry:

• Prevents the installation of add-ons requiring a higher Yoast SEO version than the current one.

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:

• Connect a site (e.g. a TasteWP site) to MyYoast (you need all the addons, not just Premium)
• install and activate Free with this change
• install and activate VideoSEO 14.8
• visit the Dashboard > Updates
  • you should see that both Free and VideoSEO can be upgraded
• Select only VideoSEO and update
• See that you get this message and VideoSEO is not updated
  
• Visit the Plugins page
• click on "update now" only for VideoSEO
• See that the update fails with the alert Update failed: The package could not be installed because it's not supported by the currently installed Yoast SEO version.
• Upload VideoSEO 14.9
• See that you get this message and VideoSEO is not updated
  
• install and activate Free 23.2-requirement-check
• try to update VideoSEO in any way and see it works now
• install and activate Premium 23.2
• visit the Dashboard > Updates
  • you should see that both Free and Premium can be upgraded
• Select only Premium and update
• See that you get this message and Premium is not updated
  
• Visit the Plugins page
• click on "update now" only for Premium
• See that the update fails with the alert Update failed: The package could not be installed because it's not supported by the currently installed Yoast SEO version.
• Upload Premium 23.3
• See that you get this message and Premium is not updated
  
• if you want, check that the above works even if Premium is not active (but Free still needs to be active for the check to be working)
• install Free 23.3-requirement-check
• try to update Premium in any way and see it works now
• Upload any Premium ZIP to overwrite the existing Premium and see that you get a new "Required Yoast SEO" row in the table outlining the plugin params:
  
• Finally, remove the feature flag or disable the small plugin and recheck the above to see that all the upgrades are allowed now instead.

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:

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 9f4d5f5aa3bacc68033d00cc2139d47a089ae1a2

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-3.1%) to 54.497%

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Totals
Change from base Build e337c625423e04fa765fac8bb295562111782b76:	-3.1%
Covered Lines:	30157
Relevant Lines:	55765

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💛 - Coveralls