Fix downloading patch reject bundles on Python 3.
Review Request #11847 — Created Oct. 12, 2021 and discarded
Patch reject bundle zip files were being written to a
uses native strings. This failed on Python 3.
Bundles are now written to a
BytesIO. Unit tests were updated to
ensure this works correctly on Python 2 and 3, and won't regress in the
Unit tests pass on Python 2 and 3.
Manually verified the fix on Python 3.