Tests: Update `wp_unique_filename()` unit tests to account for...

Tests: Update `wp_unique_filename()` unit tests to account for `sanitize_file_name()` removing accents.

Follow-up to [48603].

See #22363.
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git-svn-id: https://core.svn.wordpress.org/trunk@48366 1a063a9b-81f0-0310-95a4-ce76da25c4cd