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