XML-RPC: Switch to `wp_safe_remote()` when fetching a pingback URL. #33311

Job	Run time
Determine Matrix	4s
Multisite Default / Test current	12m 5s
Multisite Default / Test before	13m 23s
Single Site Memcached / Test current	13m 10s
Single Site Default / Test before	12m 54s
Multisite Memcached / Test before	13m 5s
Single Site Memcached / Test before	13m 26s
Multisite Memcached / Test current	13m 40s
Single Site Default / Test current	12m 49s
Slack Notifications / Prepare notifications	6s
Compare / Multisite Memcached	20s
Compare / Single Site Memcached	15s
Compare / Single Site Default	13s
Compare / Multisite Default	14s
Slack Notifications / Success notifications	6s
Slack Notifications / Cancelled notifications	-1s
Slack Notifications / Fixed notifications	-1s
Slack Notifications / Failure notifications	-1s
Failed workflow tasks	0s
	1h 45m 47s

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