add python3-six as apt dependency

Dockerfile

@@ -3,7 +3,7 @@ FROM docker.io/debian:bullseye-slim
 # install imagetagger system dependencies
 RUN apt-get update && \
 	apt-get install --no-install-recommends -y g++ wget uwsgi-plugin-python3 python3 python3-pip node-uglify make git \
-        python3-ldap3 python3-pkg-resources gettext gcc python3-dev python3-setuptools libldap2-dev \
+        python3-ldap3 python3-six python3-pkg-resources gettext gcc python3-dev python3-setuptools libldap2-dev \
 	    libsasl2-dev nginx pipenv
 
 # add requirements file