Media: Add a doc comment for the `XML2array()` method in getID3. #56725

Job	Run time
PHP 5.6 / PHP 5.6 / Single Site slow tests	2m 3s
PHP 7.3 / PHP 7.3 / Single Site with memcached	4m 25s
PHP 7.0 / PHP 7.0 / Multisite	3m 56s
PHP 7.3 / PHP 7.3 / Multisite with memcached	4m 46s
PHP 5.6 / PHP 5.6 / Multisite	5m 26s
PHP 5.6 / PHP 5.6 / Multisite slow tests	2m 1s
PHP 7.3 / PHP 7.3 / Multisite	3m 57s
PHP 5.6 / PHP 5.6 / Single Site	5m 19s
PHP 7.0 / PHP 7.0 / Single Site	3m 56s
PHP 7.3 / PHP 7.3 / Single Site	3m 34s
Slack Notifications / Prepare notifications	5s
Slack Notifications / Success notifications	6s
Slack Notifications / Fixed notifications	0s
Slack Notifications / Failure notifications	0s
Slack Notifications / Cancelled notifications	0s
Failed workflow tasks	0s
	39m 34s

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