Add test file for draft pull requests

[willschlitzer]

As discussed in #584, this is a change of the .yaml files to create a test for draft pull requests. In a draft, the tests only run Python 3.9 on Ubuntu-latest. The entire test suite for different operating systems and Python versions only runs when the pull request is marked ready for review.

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst.
• Write detailed docstrings for all functions/methods.
• If adding new functionality, add an example to docstrings or tutorials.

Slash Commands

You can write slash commands (/command) in the first line of a comment to perform
specific operations. Supported slash commands are:

• /format: automatically format and lint the code
• /test-gmt-dev: run full tests on the latest GMT development version

[willschlitzer]

@seisman @weiji14 I think I did this correctly and modified the appropriate .yaml files, but I'm not sure how to test it.

EDIT: Nevermind, it appears that none of the CI tests are running.

[seisman]

In a draft, the tests only run Python 3.9 on Ubuntu-latest.

I can't say I like this.

[willschlitzer]

In a draft, the tests only run Python 3.9 on Ubuntu-latest.

I can't say I like this.

Would you recommend something differently, or not reducing the tests at all for drafts? My thought is that ubuntu typically runs the fastest, and this will provide a check on all the tests without requiring so many CI jobs for ever minor change, but still running the gamut of tests when the PR is marked ready for review.

[seisman]

@willschlitzer See #906 for the better implementation and don't forget to push the "Delete branch" button if you no longer need it.