rebuilding the vlc-ubuntu-focal docker image produce a different version of snapcraft

with current tagged version:

> docker run --rm registry.videolan.org/vlc-ubuntu-focal:20211020115724 snapcraft --version                                       
snapcraft, version '5.0'
$> docker run --rm registry.videolan.org/vlc-ubuntu-focal:20211020115724 cat /snap/snapcraft/current/meta/snap.yaml  | grep version
version: '5.0'

if I rebuild the docker image locally, the snapcraft version is not the same

$> cd vlc-ubuntu-focal
$> docker build .
[...]
Successfully built b4706388a0cc
$> docker run --rm b4706388a0cc  cat /snap/snapcraft/current/meta/snap.yaml  | grep version
version: 6.0.2
>

and the produced snapcraft doesn't launch

$> docker run --rm b4706388a0cc  snapcraft --version                                       
Traceback (most recent call last):
  File "/snap/snapcraft/current/bin/snapcraft", line 5, in <module>
    from snapcraft.cli.__main__ import run
ModuleNotFoundError: No module named 'snapcraft'