Fix GitHub actions

[BookGin]

This PR fixed the dependency issues that causes CI test to fail.

Unless isso explicitly supports Windows and PyPy3, I don't think we should include them in the CI test.
Also we should consider drop the support for Python 3.5 which reached end-of-life.

So, I think we can discuss the following changes:

• 1. Drop support for Python 3.5. I can create a another PR for this.
• 2. Consider remove Windows tests
• 3. Consider remove PyPy tests
• 4. Consider remove MacOS tests, even though it works out of the box 😃
• 5. Add Python 3.9, which is currently latest Python

[jelmer]

Dropping support for Pytohn 3.5 LGTM.

I think we should support pypy3; perhaps we can just ignore the test results from pypy3 for now?

[BookGin]

Sure, how about Windows, MacOS and Python 3.9? (See the comment above.)

[jelmer]

I think we should run the tests for Windows and Mac OS but ignore the results for now. It would be good to include python3.9.

[BookGin]

I've included Python 3.9. For dropping support for Python 3.5. I'll create another PR.

[aquatix]

Is there something keeping these improvements from being merged?

[jelmer]

Thanks for the ping. No reason for not merging other than lack of time.

I think we should drop the broken environments as suggested in the PR description, happy to do PRs that do so.