Tests: Update the `es_ES` string used in `wp_send_user_request()` tests to...

Tests: Update the `es_ES` string used in `wp_send_user_request()` tests to match the current translation.

Props a2hosting.
Fixes #50741.
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git-svn-id: https://core.svn.wordpress.org/trunk@48343 1a063a9b-81f0-0310-95a4-ce76da25c4cd