SNAP: replace lxml versions to be compatible with Beremiz.

Forcing ubuntu20 python-lxml (4.5.0) package instead of PIP vesrion (4.9.1).
4.9.1 leads to derived variable types to appear as "derived" instead of real type name.
Problem happens with plcopen/variables_infos.ysl2 and plcopen/VariableInfoCollector.py.
No clue for now about what really breaks.

#!/bin/bash

set -e

OWNDIRBASENAME=$(basename $(cd $(dirname "${BASH_SOURCE[0]}") && pwd))

echo "Building docker image"
docker build \
    --build-arg UID=$(id -u) \
    --build-arg GID=$(id -g) \
    --build-arg OWNDIRBASENAME="$OWNDIRBASENAME" \
    -t beremiz_public_builder .