Add checking GMT Legacy/Dev Tests to the release checklist

[seisman]

Description of proposed changes

Related to #2281 (comment).

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 wrapping a new module, open a 'Wrap new GMT module' issue and submit reasonably-sized PRs.
• If adding new functionality, add an example to docstrings or tutorials.
• Use underscores (not hyphens) in names of Python files and directories.

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

[seisman]

We can wait until the GMT team decides if a Mastodon account will be created (c.f. #2244 (comment)).

[seisman]

We can wait until the GMT team decides if a Mastodon account will be created (c.f. #2244 (comment)).

No progress on the Mastodon account and we're going to make a new PyGMT release. So now it's time to review/merge this PR.

[weiji14]

We can wait until the GMT team decides if a Mastodon account will be created (c.f. #2244 (comment)).

No progress on the Mastodon account and we're going to make a new PyGMT release. So now it's time to review/merge this PR.

Thanks for the reminder. I've added the Mastodon account discussion to the agenda for the upcoming PyGMT Community Meeting at https://forum.generic-mapping-tools.org/t/pygmt-community-meeting-tuesday-14-march-2023-utc-1800/3734.