Flaky test: `downloader::test::cancellation`

[matheus23]

Log archive:
logs_31473131543.zip

First error message:

failures:
    downloader::test::cancellation

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 64 filtered out; finished in 0.75s


--- STDERR:              iroh-blobs downloader::test::cancellation ---
thread 'local-pool-7' panicked at src\downloader.rs:643:18:
assertion `left == right` failed: active_requests and in_progress_downloads are out of sync
  left: 1
 right: 2