async loopback site health test fails on alternative setups

[Levdbas]

In changeset [49917] site_url() was used to work with the new REST api tests.
This causes errors in alternative setups like Bedrock where site_url() points to example.com/wp/ which causes an error on the front-end of the website.

Changing site_url() to home_url() fixes this issue.

[peterwilsoncc]

Thanks @Levdbas, I've uploaded 52547.diff​ which makes the change you suggested.

Manually tested on a sub-directory install locally and all seems good.

[peterwilsoncc]

In 50381:

Site Health: Use home page for loopback test.

Use home_url() for asynchronous loopback test to ensure correct results on sites with WordPress installed elsewhere, for example WordPress in a sub-directory.

Props Levdbas.
Fixes #52547.

[TimothyBlynJacobs]

Reopening ​per-discussion in #core-site-health. The intent of using site_url was to more closely mimic how a cron request works. So we need to find a way to keep this close to testing loopback for cron, but not error out on subdirectory installs.

Per discussion with @peterwilsoncc, ( see above ), it looks like the best way to do this would be to make a POST request to site_url( 'wp-cron.php' ). Making this a POST request allows us to quickly exit out of Cron without triggering any cron jobs which might error out since cron would have just been executed when Site Health itself is loaded.

https://core.trac.wordpress.org/ticket/52547

[peterwilsoncc]

In 50399:

Site Health: Update loopback test to POST to wp-cron.

Replace loopback health check URL with a POST request to wp-cron.php in the WordPress install directory. This more closely represents how WordPress uses loopback requests.

A POST request is used to cause wp-cron.php to exit prior to running any cron jobs. This allows the test to indicate success quicker and accounts for sites that set the DISABLE_WP_CRON constant to avoid running cron jobs on loopback requests.

Props clorith, peterwilsoncc, TimothyBlynJacobs.
Fixes #52547.

Merged with changeset https://core.trac.wordpress.org/changeset/50399