Add tests to the `WP_Block_Styles_Registry` #28239

Job	Run time
Determine Matrix	3s
Single Site Memcached / Test current	14m 38s
Single Site Memcached / Test before	14m 51s
Single Site Default / Test before	15m 33s
Multisite Memcached / Test before	14m 56s
Multisite Default / Test current	15m 29s
Multisite Memcached / Test current	14m 13s
Multisite Default / Test before	14m 41s
Single Site Default / Test current	16m 24s
Slack Notifications	0s
Compare / Single Site Default	11s
Compare / Single Site Memcached	13s
Compare / Multisite Memcached	13s
Compare / Multisite Default	13s
Failed workflow tasks	0s
	2h 1m 38s

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