Feature/enabling python 3 9

[GabrielAzevedoFerreiraQB]

Motivation and Context

Please merge https://github.com/quantumblacklabs/causalnex/pull/156 first

Why was this PR created?

How has this been tested?

What testing strategies have you used?

Checklist

• [ ] Read the contributing guidelines
• [ ] Opened this PR as a 'Draft Pull Request' if it is work-in-progress
• [ ] Updated the documentation to reflect the code changes
• [ ] Added a description of this change and added my name to the list of supporting contributions in the RELEASE.md file
• [ ] Added tests to cover my changes
• [ ] Assigned myself to the PR

Notice

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