Update Ubuntu PPA domain

Ubuntu PPA domains changed in 2022; although the old ones were supposed to
remain indefinitely, they're currently inaccessible; but we should update to
the new one anyway

https://blog.launchpad.net/ppa/new-domain-names-for-ppas

.devcontainer/Dockerfile

@@ -9,7 +9,7 @@ RUN rm -f /etc/apt/apt.conf.d/docker-clean
 # Install python 3.10. This is the version used by the python-docker 
 # image, used for analyses using the OpenSAFELY pipeline.
 RUN --mount=type=cache,target=/var/cache/apt \
-    echo "deb http://ppa.launchpad.net/deadsnakes/ppa/ubuntu focal main" > /etc/apt/sources.list.d/deadsnakes-ppa.list &&\
+    echo "deb http://ppa.launchpadcontent.net/deadsnakes/ppa/ubuntu focal main" > /etc/apt/sources.list.d/deadsnakes-ppa.list &&\
     /usr/lib/apt/apt-helper download-file 'https://keyserver.ubuntu.com/pks/lookup?op=get&search=0xf23c5a6cf475977595c89f51ba6932366a755776' /etc/apt/trusted.gpg.d/deadsnakes.asc &&\
     apt update &&\
     apt install -y curl python3.10 python3.10-distutils python3.10-venv &&\