Let pygmt.show_versions show GDAL version

[seisman]

Description of proposed changes

Show GDAL version in pygmt.show_versions, addressing #3338 (comment).

>>> pygmt.show_versions()
PyGMT information:
version: v0.12.1.dev87+g318a8c4af
System information:
python: 3.12.4 | packaged by conda-forge | (main, Jun 17 2024, 10:11:10) [Clang 16.0.6 ]
executable: /Users/seisman/opt/miniconda/envs/pygmt/bin/python3.12
machine: macOS-14.5-x86_64-i386-64bit
Dependency information:
numpy: 2.0.0
pandas: 2.2.2
xarray: 2024.6.0
netCDF4: 1.7.1
packaging: 24.1
contextily: 1.6.0
geopandas: 1.0.1
IPython: 8.26.0
rioxarray: 0.17.0
gdal: 3.9.1
ghostscript: 10.03.1
GMT library information:
version: 6.5.0
padding: 2
share dir: /Users/seisman/opt/miniconda/envs/pygmt/share/gmt
plugin dir: /Users/seisman/opt/miniconda/envs/pygmt/lib/gmt/plugins
library path: /Users/seisman/opt/miniconda/envs/pygmt/lib/libgmt.dylib
cores: 8
grid layout: rows
image layout:
binary version: 6.5.0