Previously, if a temporary file was created, but the same data was later intended to be permanent (e.g. a temporary project icon created for the Edit Picture page was assigned to a project for continued use), the existing temporary file would be retrieved by content hash, and then later cleaned up by the garbage collector undesirably. This change adjusts the file expiry time when retrieving exising files by content hash so they live as long as if the file did not exist but were newly created.
Fixes T10907.