Improve tests for get_blog_id_from_url()

Expand tests to cover additional cache and lookup scenarios. Explicitly test the reaction of `get_blog_id_from_url()` when `$drop = false` is passed to `wpmu_delete_blog()`. See #30080

Fixes #30088

Built from https://develop.svn.wordpress.org/trunk@30007


git-svn-id: http://core.svn.wordpress.org/trunk@30007 1a063a9b-81f0-0310-95a4-ce76da25c4cd