wp-admin/includes/class-automatic-upgrader-skin.php:61Retrieves the upgrade messages.
string[] public function get_upgrade_messages() { return $this->messages; }Introduced in 3.7.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-admin/includes/class-automatic-upgrader-skin.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.