CI: Use macos-13 for Tests Dev workflow and consistently use lower-case runner names

[seisman]

Description of proposed changes

1. Use macos instead of macOS for runner names, following the official documentation
2. Use macos-13 instead of macos-12 in the "Tests Dev" workflow

Reference: https://github.blog/changelog/2023-04-24-github-actions-macos-13-is-now-available/

Fixes #

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]

All workflows still pass. Need to update the branch protection rules after merging.

[weiji14]

Cool, so according to https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners#supported-runners-and-hardware-resources, GitHub Actions currently has 3 runners for macOS:

• macos-11 Big Sur - used in ci_tests_legacy.yaml
• macos-12/macos-latest Monterey - used in most of our ci_*.yml files
• macos-13 Ventura [Beta] - used in ci_tests_dev.yaml

Looks ok to me!