XML-RPC: Switch to `wp_safe_remote()` when fetching a pingback URL. #33298

Job	Run time
Determine Matrix	3s
Multisite Default / Test 6.7.0	12m 13s
Multisite Memcached / Test 6.7.0	12m 35s
Single Site Default / Test current	14m 0s
Single Site Default / Test 6.7.0	12m 2s
Single Site Memcached / Test 6.7.0	12m 45s
Single Site Memcached / Test current	12m 51s
Multisite Default / Test current	13m 6s
Multisite Memcached / Test current	13m 19s
Slack Notifications / Prepare notifications	4s
Compare / Single Site Memcached	32s
Compare / Single Site Default (Publishes)	16s
Compare / Multisite Memcached	31s
Compare / Multisite Default	27s
Slack Notifications / Success notifications	3s
Slack Notifications / Cancelled notifications	0s
Slack Notifications / Failure notifications	0s
Slack Notifications / Fixed notifications	0s
Failed workflow tasks	0s
	1h 44m 47s

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