Run GMT Dev Tests on Monday, Wednesday and Friday only

[weiji14]

Description of proposed changes

Updating the cron tab to run GMT Dev Tests on Monday/Wednesday/Friday instead of daily. A bit annoying to have the tests failing everyday, especially during the weekend. See also #1833 (comment) about having less frequent tests.

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.

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

[weiji14]

FYI, macOS tests breaking due to blosc (which gdal depends on) no longer packaging ZSTD, see #1923

pygmt.exceptions.GMTCLibNotFoundError: Error loading GMT shared library at '/Users/runner/miniconda3/envs/pygmt/lib/libgmt.dylib'.
dlopen(/Users/runner/miniconda3/envs/pygmt/lib/libgmt.dylib, 6): Symbol not found: _ZSTD_compressBound
  Referenced from: /Users/runner/miniconda3/envs/pygmt/lib/libgdal.30.dylib
  Expected in: /Users/runner/miniconda3/envs/pygmt/lib/libblosc.1.dylib
 in /Users/runner/miniconda3/envs/pygmt/lib/libgdal.30.dylib
Error loading GMT shared library at 'libgmt.dylib'.
dlopen(libgmt.dylib, 6): Symbol not found: _ZSTD_compressBound
  Referenced from: /Users/runner/miniconda3/envs/pygmt/lib/libgdal.30.dylib
  Expected in: /Users/runner/miniconda3/envs/pygmt/lib/libblosc.1.dylib
 in /Users/runner/miniconda3/envs/pygmt/lib/libgdal.30.dylib