CI: Test NumPy 2.0 in the GMT Tests workflow

[seisman]

Description of proposed changes

Bumps numpy from 1.26 to 2.0. NumPy 2.0.0 was released on 17 Jun 2024.

• Release notes
• Changelog
• Commits

This is in line with PyGMT's policy on SPEC0 at https://www.pygmt.org/v0.12.0/maintenance.html#dependencies-policy, xref #2863.

Note that the branch protection rules at GenericMappingTools/pygmt/settings/branches will need to be changed to use Python 3.12/Numpy 2.0 instead of Python 3.12/Numpy 1.26 before this Pull Request is merged.

Supersedes #2692

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

[weiji14]

This was almost too easy for a major version bump!