Enable CI testing with GitHub Action

[avalentino]

• Enable Continuous Integration (CI) testing with GitHub Action (GHA)
• update min pytest version for compatibility with Python 3.10
• Update classifier to declare support for Python 3.8, 3.9 and 3.10

[bmcfee]

Thanks for this! I've been meaning to modernize testing and packaging across my various projects, so this is much appreciated.

Is there an easy way to test-drive this action before merging?

[avalentino]

The last run on my fork is at the following URL: https://github.com/avalentino/resampy/actions/runs/2200166742

[avalentino]

Thanks for merging @bmcfee