Release 2.0.0a4 - alpha quality, for testing only

borgbackup 2.0.0a4 alpha release - do not use this on production backup repositories.

Long changelog:
https://borgbackup.readthedocs.io/en/2.0.0a4/changes.html#version-2-0-0a4-2022-07-17

If you use pip to install this, use: pip install "borgbackup==2.0.0a4"

Docs: https://borgbackup.readthedocs.io/en/2.0.0a4/

Feedback:

• discussion: #6872