Dockerfile: Add a focal workaround through a sed hack

Author: C0rn3j

Dockerfile

@@ -8,7 +8,8 @@ RUN <<EOR
 	set -eu
 
 	# Workaround for outstanding fix of https://bugs.launchpad.net/ubuntu/+source/python-build/+bug/1992108
-	if grep -q ^UBUNTU_CODENAME=jammy /etc/os-release; then
+	. /etc/os-release
+	if [ ${UBUNTU_CODENAME} = 'jammy' ]; then
 		echo >>/etc/apt/sources.list.d/jammy-proposed.list 'deb [arch=amd64] http://archive.ubuntu.com/ubuntu/     jammy-proposed universe'
 		echo >>/etc/apt/sources.list.d/jammy-proposed.list 'deb [arch=arm64] http://ports.ubuntu.com/ubuntu-ports/ jammy-proposed universe'
 	fi
@@ -48,6 +49,12 @@ ARG TARGET=/build
 RUN <<EOR
 	set -eu
 
+	# Focal workaround, until it is removed completely, builds a semi-broken image (About does not work at minimum)
+	. /etc/os-release
+	if [ ${UBUNTU_CODENAME} = 'focal' ]; then
+		sed -i -e 's/>=3.9/>=3.8/' -e 's/py39/py38/' pyproject.toml
+	fi
+
 	python -m build --wheel
 	python -m venv .env
 	. .env/bin/activate