Embeds: Fix incorrect usage of `get_home_url()` in oEmbed tests.

Switch to `home_url()` for consistency with other tests and to avoid confusion.

Props david.binda.
Fixes #49988.
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git-svn-id: https://core.svn.wordpress.org/trunk@47390 1a063a9b-81f0-0310-95a4-ce76da25c4cd