Add support for pip>=22.1

[atugushev]

• Prepare pip-tools for the upcoming pip-22.1 release, see Release 22.1 (April 2022) pypa/pip#10991.
• Add main to the matrix so that we could see the changes pass tests. There is fail-fast: false on CI so the workflow shouldn't be failed if main fails. It would be nice to have some kind of allow-failure, but it's not yet implemented, see: Please support something like "allow-failure" for a given job actions/runner#2347.

Contributor checklist

• Provided the tests for the changes.
• Assure PR title is short, clear, and good to be included in the user-oriented changelog

Maintainer checklist

• Assure one of these labels is present: backwards incompatible, feature, enhancement, deprecation, bug, dependency, docs or skip-changelog as they determine changelog listing.
• Assign the PR to an existing or new milestone for the target version (following Semantic Versioning).

[pradyunsg]

Hurrah! Thanks for picking this up. I have a very minor suggestion.

[ssbarnea]

I requests @pradyunsg to update its review so I will wait for his comment or approval before merging. That is a very welcomed addition.

[pradyunsg]

Please feel free to merge this without waiting on my review. If I have time to do a review, I’ll do one. :)

[atugushev]

Thanks @duoi and @ssbarnea for the review! I'm gonna merge this then.