Wrong usage of mysql2date to generate datePublished and dateModified, bug in time offsets

[DrLightman]

As the WordPress's mysql2date() PHP doc says:

$date is expected to be local time in MySQL format ('Y-m-d H:i:s').

Please note "local time", not GMT time.

Whereas the AMP plugin uses the GMT values instead, resulting in wrong values in datePublished and dateModified attributes of schemaorg metadata:

[
	'@type'            => is_page() ? 'WebPage' : 'BlogPosting',
	'mainEntityOfPage' => get_permalink(),
	'headline'         => get_the_title(),
	'datePublished'    => mysql2date( 'c', $queried_object->post_date_gmt, false ),
	'dateModified'     => mysql2date( 'c', $queried_object->post_modified_gmt, false ),
]

The resulting datePublished will be wrongly comprised of a datetime local to GMT combined with a not zero offset.
The solution is to remove the _gmt parts from the properties:

[
	'@type'            => is_page() ? 'WebPage' : 'BlogPosting',
	'mainEntityOfPage' => get_permalink(),
	'headline'         => get_the_title(),
	'datePublished'    => mysql2date( 'c', $queried_object->post_date, false ),
	'dateModified'     => mysql2date( 'c', $queried_object->post_modified, false ),
]

[pierlon]

Note that this bug only occurs in WP 5.3 and above, as mysql2date() now makes use of the wp_timezone() function (introduced in WP 5.3) that returns the site's timezone setting.

[westonruter]

Related: #5335

[pierlon]

(QA comment: #6318 (comment))