There's a merged pull request on the void-packages repository

s3cmd: backport Python 3.9 compatibility fix
https://github.com/void-linux/void-packages/pull/26347

Description:
https://github.com/s3tools/s3cmd/issues/1146 is fixed in `master` by https://github.com/s3tools/s3cmd/pull/1137. This PR adds corresponding patch.