Install required Python versions in TestKit Docker image

Author: robsdedude

testkit/Dockerfile

@@ -42,9 +42,9 @@ ENV PYENV_ROOT /.pyenv
 ENV PATH $PYENV_ROOT/shims:$PYENV_ROOT/bin:$PATH
 
 # Set minimum supported Python version
-RUN pyenv install 3.7.12
+RUN pyenv install 3.7:latest 3.8:latest 3.9:latest 3.10:latest
 RUN pyenv rehash
-RUN pyenv global 3.7.12
+RUN pyenv global $(pyenv versions --bare --skip-aliases)
 
 # Install Latest pip for each environment
 # https://pip.pypa.io/en/stable/news/