Stefan Mallia

Update Dockerfile to use Python 3.9

3

## Description Small change to the Dockerfile to use Python 3.9 as required by pyproject.toml. Currently the docker build fails on "Package 'pgcli' requires a different Python: 3.8.20 not in...

When running the docker build command in the readme, it fails on "Package 'pgcli' requires a different Python: 3.8.20 not in '>=3.9'".