fix: workaround docker==5.0.0 not importing its dependencies

Dockerfile

@@ -11,6 +11,7 @@ RUN mkdir /tmp/wheelhouse \
  && cd /tmp/wheelhouse \
  && pip3 install wheel \
  && pip3 wheel --no-cache-dir /tmp/src \
+ && rm /tmp/wheelhouse/six*.whl \
  && ls -l /tmp/wheelhouse
 
 FROM alpine:${ALPINE_VERSION}

setup.py

@@ -57,6 +57,9 @@ setup(
         "requests",
         "ruamel.yaml>=0.15",
         "semver",
+        # six installation is a workaround of https://github.com/docker/docker-py/pull/2844.
+        # When removing this, also remove the "rm /tmp/wheelhouse/six*.whl" line in ./Dockerfile
+        "six",
         "toml",
         "traitlets",
     ],