Avoid a useless redirect with site title and home link blocks

[Chouby]

What?

Fixes #65670

Why?

Avoid a redirect caused by the link in the site title block when WordPress is installed in a sufolder or on multisite with sites in folder.

How?

Use home_url( '/' ) instead of home_url()`

Testing Instructions

1. Install WordPress in a subfolder
2. Create a page and insert the site title block
3. View the page on frontend
4. Open the browser tools to observe that there will be no redirect.
5. Check the link proposed by the site title block is https://mysite.com/wordpress/ instead of https://mysite.com/wordpress in the current stable version.
6. Click on the link and observe that there is no 301 redirect

[github-actions]

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Co-authored-by: Chouby <chouby@git.wordpress.org>
Co-authored-by: Mamaduka <mamaduka@git.wordpress.org>

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[Mamaduka]

@Chouby, do you mind rebasing your branch on top of the latest trunk? That should unblock GitHub CI checks.

See: https://developer.wordpress.org/block-editor/contributors/code/git-workflow/#keeping-your-branch-up-to-date

[Chouby]

One test is still failing :

gutenberg/phpunit/blocks/class-wp-navigation-block-renderer-test.php

Line 62 in 11f9a32

$expected = '<li class="wp-block-navigation-item"><h1 class="wp-block-site-title"><a href="http://' . WP_TESTS_DOMAIN . '" target="_self" rel="home">Test Blog</a></h1></li>';

It's not very surprising as 'http://' . WP_TESTS_DOMAIN doesn't account the fact that the home url can sometimes have a trailing slash and sometimes not.
My first idea to work around this would be to replace it by home_url( '/' ) but I usually don't like to use the same function in the test and the tested code. What do you think?