Update GitHub Actions migration to match other Jazzband projects.

[jezdez]

Description

I'm currently porting all of Jazzband projects to GitHub Actions and this
is a minor update to #738 (thank you @ThePumpingLemma!).

It does drop Python 3.5 support though since that's EOL'd now.

It also adds Jazzband releases again after it was removed in #738. @rossmechanic Please make sure to not remove it again.

Related Issue

#738
https://github.com/orgs/jazzband/projects/1

Motivation and Context

This is only needed to keep Jazzband projects close in how they are configured.

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have run the make format command to format my code
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have added my name and/or github handle to AUTHORS.rst
• I have added my change to CHANGES.rst
• All new and existing tests passed.

Original text I've used in other PRs relating to the migration to GitHub Actions:

Travis CI has a new pricing model which places limits on open source.

• https://blog.travis-ci.com/2020-11-02-travis-ci-new-billing
• https://www.jeffgeerling.com/blog/2020/travis-cis-new-pricing-plan-threw-wrench-my-open-source-works

Many projects are moving to GitHub Actions instead, including Jazzband projects:

• https://github.com/orgs/jazzband/projects/1
• Should we disable travis? help#206

This is based on jazzband/contextlib2#26.

TODO:

• @jezdez to add JAZZBAND_RELEASE_KEY to the repo secrets.

[codecov]

Codecov Report

Merging #769 (c3ac048) into master (faed6d5) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #769   +/-   ##
=======================================
  Coverage   97.47%   97.47%           
=======================================
  Files          18       18           
  Lines         992      992           
  Branches      151      151           
=======================================
  Hits          967      967           
  Misses         12       12           
  Partials       13       13           

---

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[ThePumpingLemma]

It appears that every build is running twice? Is that intentional?

[jezdez]

@ThePumpingLemma Yeah, that's expected (even if a bit broad) since we're tracking both pushes to all branches (including the pull request branch) as well as other pull request events (by default "opened", "synchronize" and "reopened").

Those pull request events basically just describe other things that can happen to a pull request during its lifetime (and after its first lifetime for that matter) so that the tests are always run in whatever state the PR is in. The "synchronize" event type happens when a pull request's branch is updated with the tracking branch (e.g. the main/master branch is merged in). Hope that explains the reasoning.

[ThePumpingLemma]

Thanks @jezdez!