panic: cannot consume from pending buffer

[sentry-io]

Sentry Issue: CRATES-IO-BACKEND-3YV

panic: cannot consume from pending buffer
  ?, in rust_begin_unwind
  ?, in object_store::buffered::BufReader::consume
  ?, in async_compression::tokio::bufread::generic::decoder::Decoder<T>::poll_read
  ?, in crates_io_cdn_logs::count_downloads::{{closure}}::{{closure}}
  ?, in tracing::instrument::Instrumented<T>::poll
...
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[Turbo87]

first up: this has only been panicking on our staging environment, not on production.

Sentry pointed out that 00b5b2e (aka. #9622) was the first release that saw this behavior, and since async_compression is involved in the stacktrace that seems like a very likely root cause.

I've opened Nullus157/async-compression#298 with a couple more details.