ITDE: Update to Python 3.9

[ckunki]

1. Update Minimum Python version in file pyproject.toml
2. Update dependencies poetry update
3. Update Matrix build definitions in files in .github/workflows especially test_python_version.yml
4. Update Ubuntu docker images (proposal: to 20.04). There are still some places using the 18.04 Ubuntu image, like:
   • heath.sh
   • docker_check_pull: https://github.com/exasol/integration-test-docker-environment/blob/a77a910447a9b3571f8effb0b8cfd9cf6677b81e/scripts/health.sh#L106
   • docker_check_connectivity: https://github.com/exasol/integration-test-docker-environment/blob/a77a910447a9b3571f8effb0b8cfd9cf6677b81e/scripts/health.sh#L120
   • spawn_test_database.py
   • test_analyze_image/Dockerfile
   • test_test_container_reuse/tests/Dockerfile
   • test_api_test_environment_docker_environment.py
5. Update Docker image for start scripts and test test containers from Ubuntu 20.04 to Ubuntu 22.04

[Nicoretti]

@ckunki, we likely only can bump it to 3.9, depending on whether we upgrade all projects to 3.10 or not. Since itde is used in almost every Python-based project that conducts integration tests, we need it to support the lowest version these projects work on.