unsupported msgpack version

[laulau]

HI ;
since a few days borg stopped working :

# borg help
You do not have a supported version of the msgpack python package installed. Terminating.
This should never happen as specific, supported versions are required by our pyproject.toml.
Do not contact borgbackup support about this.
Error: unsupported msgpack version

# borg --version
borg 1.4.0

# apt show borgbackup
Package: borgbackup
Version: 1.4.0-1~bpo20.04.1~ppa4
Priority: optional
Section: admin
Maintainer: Debian Borg Collective <email address hidden>
Installed-Size: 3,573 kB
Depends: python3-pkg-resources, python3 (<< 3.9), python3 (>= 3.8~), python3-msgpack, python3-packaging, python3:any, libacl1 (>= 2.2.51), libc6 (>= 2.14), liblz4-1 (>= 0.0~r130), libssl1.1 (>= 1.1.0), libxxhash0 (>= 0.6.5), libzstd1 (>= 1.3.2)
Recommends: fuse3
Suggests: python3-pyfuse3, borgbackup-doc
Download-Size: 844 kB
APT-Manual-Installed: yes
APT-Sources: http://ppa.launchpad.net/costamagnagianfranco/borgbackup/ubuntu focal/main amd64 Packages

# apt show python3-msgpack
Package: python3-msgpack
Version: 0.6.2-1
Priority: optional
Section: python
Source: python-msgpack
Origin: Ubuntu
Maintainer: Ubuntu Developers <email address hidden>
Original-Maintainer: Debian OpenStack <email address hidden>
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
Installed-Size: 249 kB
Depends: python3 (<< 3.9), python3 (>= 3.8~), python3:any, libc6 (>= 2.14)
Homepage: https://pypi.python.org/pypi/msgpack
Task: ubuntustudio-publishing
Download-Size: 73.5 kB
APT-Manual-Installed: yes
APT-Sources: http://mirrors.online.net/ubuntu focal/main amd64 Packages