Coding Standards: Use a strict `in_array()` check for reserved names of user...

Coding Standards: Use a strict `in_array()` check for reserved names of user data items in `wp_user_personal_data_exporter()`.

Props azaozz.
Fixes #47509.
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git-svn-id: https://core.svn.wordpress.org/trunk@47077 1a063a9b-81f0-0310-95a4-ce76da25c4cd