- Adds docker-build-test job to regression.yml
- Runs on push/merge to master and release branches
- Extracts VERSION_TAG from pyproject.toml for build
- Tests that Docker image builds and runs successfully
- Resolves dockerfile syntax warnings
- Resolves#2196"
Python 3.8 is nearing EOL, and it's being deprecated here to allow for
more ready dependency resolution between pandas and numpy, avoiding a
fatal import. Resolves#2266.