Fix wrong error `TorrentNotFound` added to logs when Tracker API token is invalid

[josecelano]

Relates to: #419

I've been checking the logs of the live demo. It's failing because the tracker token is not valid:

2023-12-26T11:00:35.187361844+00:00 [torrust_index::tracker::statistics_importer][INFO] Updating torrent 1 ...
2023-12-26T11:00:35.233911132+00:00 [torrust_index::tracker::service][ERROR] Failed to parse torrent info from tracker response. Body: Unhandled rejection: Err { reason: "token not valid" }
2023-12-26T11:00:35.242595113+00:00 [torrust_index::tracker::statistics_importer][ERROR] Error updating torrent tracker stats for torrent with id 1: TorrentNotFound

There are two issues:

• Invalid token: Token not valid
• Wrong logged error: TorrentNotFound

Wrong logged error

The second issue is that all tracker API errors are written into the log as TorrentNotFound errors. That was already documented with a code-review comment in the code:

    pub async fn import_all_torrents_statistics(&self) -> Result<(), database::Error> {
        info!("Importing torrents statistics from tracker ...");
        let torrents = self.database.get_all_torrents_compact().await?;

        for torrent in torrents {
            info!("Updating torrent {} ...", torrent.torrent_id);

            let ret = self.import_torrent_statistics(torrent.torrent_id, &torrent.info_hash).await;

            // code-review: should we treat differently for each case?. The
            // tracker API could be temporarily offline, or there could be a
            // tracker misconfiguration.
            //
            // This is the log when the torrent is not found in the tracker:
            //
            // ```
            // 2023-05-09T13:31:24.497465723+00:00 [torrust_index::tracker::statistics_importer][ERROR] Error updating torrent tracker stats for torrent with id 140: TorrentNotFound
            // ```

            if let Some(err) = ret.err() {
                let message = format!(
                    "Error updating torrent tracker stats for torrent with id {}: {:?}",
                    torrent.torrent_id, err
                );
                error!("{}", message);
            }
        }

        Ok(())
    }

We should log the right reason.