#38231 added support for files fetched remotely to have their filename defined by the host using the `Content-Disposition` header. This would then take priority over the existing temporary file name created with `wp_tempnam()` earlier in the process.
The change unintentionally omitted the temporary directory path used during uploads, since the `wp_tempnam()` function would have added it previously, so that files with this header ended up being stored in the WordPress root folder, or wp-admin folder, when triggered by WP_Cron or user interactions respectively.
This change makes sure the file path includes the temporary directory location when the header is used.
Follow-up to [51939].
Props antonynz, azouamauriac.
Fixes#55109.
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