[New] Drop Python 3.8 support

[lisphilar]

Checkbox

• [X] I agree to follow code of conduct and to engage in discussion actively.
• [X] I used the latest version of covsirphy.

Summary

Drop Python 3.8 support.

Solutions

No response

APIs to be deprecated

No response

Additional Context

No response

[lisphilar]

• This is related to #1592.
• Specify the latest versions (usable in Google Colab) of the dependencies.