Add deployment/testing with Python 3.10

[SteveDiamond]

No description provided.

[SteveDiamond]

@phschiele @akshayka I'm getting pretty close to getting 3.10 working. I'm getting a weird bug I can't reproduce locally involving diffcp: https://github.com/cvxpy/cvxpy/runs/4628602909?check_suite_focus=true#step:6:4333
I'll think about it more but if anything comes to mind let me know.

Edit: Looks like SCS is failing to solve the problem...

[phschiele]

@SteveDiamond I think I found the issue:
Installing diffcp under Python 3.10 installs 1.0.16 instead of 1.0.18, which does not have support for SCS 3.0 yet.
The reason is that on PyPI there are neither wheels for 3.10, nor the source.
I'll check why the source was not deployed with the last tag. After this is fixed, the tests should pass here, and you could even undo the changes made to diffcp_conif.py, as this is handled within diffcp.

[phschiele]

@SteveDiamond I found two more occurrences where the Python versions are listed explicitly: pyproject.toml and sonar-project.properties.

[SteveDiamond]

@phschiele thanks so much for figuring it out! I'm also having some problems building wheels for 3.10. Not totally sure what's going on there: https://github.com/cvxgrp/diffcp/runs/4632902674?check_suite_focus=true#step:7:53

Edit: I tried fixing this by upping the cibuildwheel version, but then windows builds failed :(

[SteveDiamond]

Integrating a version of #1559

[SteveDiamond]

@phschiele I think this is good to go. Could you review it when you have time?

Edit: Nvm, it's failing to build wheels on ubuntu.

[phschiele]

@SteveDiamond This looks good 🚀
I hade one small remark about the diffcp interface above.

A second detail is that some of the environment variables like the PyPI settings are now unused in the build workflow and could be removed there.

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
1 Code Smell

100.0% Coverage
0.0% Duplication

[phschiele]

@SteveDiamond Just a reminder to undo these shortcuts after everything is confirmed working.

[SteveDiamond]

Thanks! I'm going to let it build the wheels once on master and then undo them.