fix: SEO site-title tag for homepage

[preda-bogdan]

Summary

Changed the tag for site-title on mobile to use p instead of h1 the same as for all other pages where the site title should not be the main title. SEO will now see only the h1 used by the desktop on the homepage where usually no other main title is present.

Will affect the visual aspect of the product

NO

Screenshots

Test instructions

1. Create a new instance with Neve and set the home page to your latest posts
2. Add the Logo & Site Identity component
3. Set a site title if not already set
4. Enable Show Site Title
5. Check on the front-end homepage that only one h1 tag is present.

Check before Pull Request is ready:

• I have written a test and included it in this PR
• I have run all tests and they pass
• The code passes when running the PHP CodeSniffer
• Code meets WordPress Coding Standards for PHP, HTML, CSS and JS
• Security and Sanitization requirements have been followed
• I have assigned a reviewer or two to review this PR (if you're not sure who to assign, we can do this step for you)

Closes #3984.

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[irinelenache]

@preda-bogdan Tested and the issue is fixed now 👍

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🎉 This PR is included in version 3.8.0 🎉

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