Migrate to GitHub Actions

[pcrov]

Travis's open source support has recently diminished. In short open source projects will get a bucket of minutes to work with and can manually reapply for a refill as needed however their requirements to qualify have changed.

Github Actions has its warts but at least it gives a bucket of minutes every month that you don't have to reapply for.

Anyway, this PR aims to kick travis to the curb and tick off some boxes in #47 in the process. In particular:

• [x] Test with lowest deps
• [x] Test with highest deps
• [x] Test with php 8
• [x] Set up phpcs

You can see the results at https://github.com/pcrov/gitamp/actions.

Next up, to make checks green.

• [x] Fix lowest deps
  • [x] PHP 7.4, 8.0 - tests fail, find a min version of something to bump.
  • [x] PHP 8.0 - PHPUnit itself fails, bump min version.
• [x] PHP 8.0
  • [x] Uploading coverage to Scrutinizer fails. Their ocular.phar is incompatible with PHP 8, skipping coverage on this version.
  • [x] Tests for non-lowest deps pass (yay) when force installed with --ignore-platform-req=php. Without it install fails complaining about maglnet/composer-require-checker. Pull from require-dev and let CI handle grabbing the tool
• [x] phpcs is running and reporting errors, set continue-on-error so that the workflow succeeds even on failure of this job. TODO: fix the coding or fix the standards.

[pcrov]

BTW, If someone wants to check the current errors and verify which standards in the phpcs config are actually desired I can fix things up to a passing baseline.

[ekinhbayar]

Hey @pcrov o/ This looks awesome! I'm going to merge this PR and cross check the CS config and code later on.

Thanks a lot for setting it all up and apologies for how long it took me to review all this <3 Busy times...

[pcrov]

No worries. Feel free to ping me if it gives you any trouble. Cheers :)