Supporting python 3.6 & 3.9 in CI

[you-n-g]

🐛 Bug Description

To Reproduce

Install Qlib under 3.6 & 3.9 in CI

Expected Behavior

The CI fails.

Screenshot

Environment

Note: One could run python scripts/collect_info.py under the qlib directory to get the following information.

• Qlib version:
• Python version:
• OS (Windows, Linux, MacOS):
• Commit number (optional, please provide it if you are using the dev version):

Additional Notes