Unpin geopandas 0.13.0 in CI docs build

[weiji14]

Description of proposed changes

The issue of reading zip files from URLs should have been resolved in geopandas>=0.13.1, see geopandas/geopandas@v0.13.0...v0.13.2

Preview at https://pygmt-dev--2568.org.readthedocs.build/en/2568/gallery/lines/roads.html#sphx-glr-gallery-lines-roads-py

Reverts #2545

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

[weiji14]

Hold on, the Readthedocs build at https://readthedocs.org/projects/pygmt-dev/builds/20952470/ seems to be stuck.

Edit: Readthedocs build completed. Can confirm that the example downloading the zip file at https://pygmt-dev--2568.org.readthedocs.build/en/2568/gallery/lines/roads.html#sphx-glr-gallery-lines-roads-py works now.