Update in-product webinar banner copy on admin pages

[JorPV]

Context

This PR updates the webinar promotional banner copy displayed to free Yoast SEO users on admin pages.

This PR can be summarized in the following changelog entry:

• Updates the webinar promotion banner copy on admin pages.

Relevant technical choices

• Used safeCreateInterpolateElement with sprintf to render FREE in bold (<strong>), following the same pattern used across the integrations page components.
• The shortlink URL and "Sign up today!" call-to-action remain unchanged.

Test instructions for the acceptance test before the PR gets merged

1. Install and activate the free Yoast SEO plugin (make sure Premium is not active).
2. Go to any admin page where the webinar promo banner appears (e.g., Posts > Add New and open the Yoast SEO sidebar, or visit the Yoast SEO dashboard).
3. If you have previously dismissed the banner, reset it by clearing the webinar-promo-notification dismissal (e.g., via the browser console or by resetting the user meta).
4. Verify the banner now shows:
   • Header: "Ready to boost your online visibility?"
   • Body: "Access our FREE webinars and podcasts to get started with Yoast SEO and build the foundational skills and confidence needed for sustainable success. Sign up today!"
   • The word FREE should be displayed in bold.
   • The "Sign up today!" link should still work and open in a new tab.
5. Verify the banner does not appear when Yoast SEO Premium is active.

Relevant test scenarios

• 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 with the browser console open
• Changes should be tested on different browsers
• Changes should be tested on multisite

The banner appears in both the block editor sidebar and settings pages — verify the copy is correct in both contexts.

Test instructions for QA when the code is in the RC

• QA should use the same steps as above.

Impact check

• The webinar promotional notification component (WebinarPromoNotification.js) used on admin pages for free users.

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.
• This PR also affects Yoast SEO for Google Docs. I have added a changelog entry starting with [yoast-doc-extension], added test instructions for Yoast SEO for Google Docs and attached the Google Docs Add-on label to this PR.

Documentation

• I have written documentation for this change.

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.
• I have run grunt build:images and commited the results, if my PR introduces new images or SVGs.

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 Yoast/reserved-tasks#1108

[coveralls]

Pull Request Test Coverage Report for Build 0b46e9b602ccf8db18e9df6412baaf93defac499

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall first build on jpv/update-in-product-webinar-banner-on-admin-pages at 32.14%

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Totals
Change from base Build c500bb9eaa82f0d0ad3b3a473ac33b1b28256339:	32.1%
Covered Lines:	5491
Relevant Lines:	16002

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💛 - Coveralls

[thijsoo]

1 small comment

[thijsoo]

Yoast SEO should be replaced wit ha % var as well.

[thijsoo]

CR + ACC 👍