stock xenial pg12 docker image and reproduce collation error

docker-xenial-pg12-setup

# Start stock xenial
> docker run -it ubuntu:xenial bash

# Prepare image
apt-get update \
&& apt-get install vim software-properties-common wget apt-transport-https

add-apt-repository -y "deb https://apt.postgresql.org/pub/repos/apt/ xenial-pgdg main" \
&& wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | apt-key add -

apt-get update \
&& apt-get install -y --no-install-recommends postgresql-common \
&& echo 'create_main_cluster = false' >> /etc/postgresql-common/createcluster.conf \
&& apt-get install -y --no-install-recommends \
postgresql-12 \
postgresql-12-dbg \
postgresql-12-pgextwlist \
postgresql-client-12 \
postgresql-contrib-12

# Update locale and make dir/files
locale-gen en_US.UTF-8 && update-locale;
mkdir /database && chown postgres /database;
touch /logfile && chown postgres /logfile;

# initdb and setup
su postgres

env                                                                   \
LC_COLLATE=en_US.UTF-8                                                \
LC_CTYPE=en_US.UTF-8                                                  \
LC_MESSAGES=en_US.UTF-8                                               \
LC_MONETARY=en_US.UTF-8                                               \
LC_NUMERIC=en_US.UTF-8                                                \
LC_TIME=en_US.UTF-8                                                   \
/usr/lib/postgresql/12/bin/initdb -D /database -E UTF8 -U postgres

mkdir -p /database/pgextwlist/pg_stat_statements && touch /database/pgextwlist/pg_stat_statements/after-create.sql;
echo "GRANT EXECUTE ON FUNCTION pg_stat_statements_reset() TO test_user;" >> /database/pgextwlist/pg_stat_statements/after-create.sql;

#Update configuration to use pgextwlist

cat <<EOF >> /database/postgresql.conf
shared_preload_libraries = 'pg_stat_statements'
local_preload_libraries = pgextwlist
extwlist.extensions = 'pg_stat_statements'
extwlist.custom_path = '/database/pgextwlist'
EOF

# Start process, create user/db
/usr/lib/postgresql/12/bin/pg_ctl -D /database -l /logfile start

psql -U postgres << EOF
CREATE ROLE test_user;
ALTER ROLE test_user WITH LOGIN PASSWORD 'test_pwd' NOSUPERUSER NOCREATEDB NOCREATEROLE;
CREATE DATABASE test_db OWNER test_user;
GRANT CONNECT ON DATABASE test_db TO test_user;
GRANT ALL ON DATABASE test_db TO test_user;
GRANT ALL ON SCHEMA public TO test_user;
EOF

# Trigger error
psql -U test_user -d test_db -c 'CREATE EXTENSION pg_stat_statements WITH SCHEMA public'