Confirming this `'core_updater.lock'`. It may not be obvious at first but look at the line `771`.

    File: wp-admin/includes/class-wp-upgrader.php
    754: 	/**
    755:  	 * Creates a lock using WordPress options.
    756:  	 *
    757:  	 * @since 4.5.0
    758:  	 * @access public
    759:  	 * @static
    760:  	 *
    761:  	 * @param string $lock_name       The name of this unique lock.
    762:  	 * @param int    $release_timeout Optional. The duration in seconds to respect an existing lock.
    763: 	 *                                Default: 1 hour.
    764:  	 * @return bool False if a lock couldn't be created or if the lock is no longer valid. True otherwise.
    765:  	 */
    766: 	public static function create_lock( $lock_name, $release_timeout = null ) {
    767: 		global $wpdb;
    768: 		if ( ! $release_timeout ) {
    769: 			$release_timeout = HOUR_IN_SECONDS;
    770: 		}
    771: 		$lock_option = $lock_name . '.lock';
    772: 
    773: 		// Try to lock.
    774: 		$lock_result = $wpdb->query( $wpdb->prepare( "INSERT IGNORE INTO `$wpdb->options` ( `option_name`, `option_value`, `autoload` ) VALUES (%s, %s, 'no') /* LOCK */", $lock_option, time() ) );
    775: