Refactor workflows

[astrofrog]

This refactors the workflows into:

• A workflow that will only run on cron and workflow_dispatch - this workflow will update the files to the latest versions, run the tests on Linux, push the changes to the repository if the tests pass, run the tests on all platforms just to double check, tag the calendar version, and publish to PyPI. The tagging and publishing only happen if the tests succeed on all platforms. There are several benefits to this workflow:
  • The tests will actually run when updating the IERS files and before committing. Currently with the PR model, the maintainer needs to know to close and open the PR to trigger the CI.
  • No manual step of reviewing and merging every week
  • Fixes https://github.com/astropy/astropy-iers-data/issues/10
• A workflow that will only run on push and pull_request and simply runs the tests on all platforms

If we want to keep publishing Zenodo releases, I will need to add a step to automatically create the release after the tag is pushed - it would be easier to add this in a follow-up PR once we know the rest is working properly.

Fixes https://github.com/astropy/astropy-iers-data/issues/5

[astrofrog]

I've opened an issue at https://github.com/astropy/astropy-iers-data/issues/15 to remember to automate the GitHub release + Zenodo

[astrofrog]

@pllim - are you interested in reviewing this? Or should I just merge?