Add small grid based on earth_relief_01d V2.3

[maxrjones]

Based on discussions from https://github.com/GenericMappingTools/pygmt/issues/1684, this PR adds a small file based on earth_relief_01d to the cache. This file will be used for PyGMT tests so that those tests do not need to be updated following earth_relief updates.

Here is the file contents:

netcdf static_earth_relief {
dimensions:
    lon = 8 ;
    lat = 14 ;
variables:
    double lon(lon) ;
        lon:long_name = "longitude" ;
        lon:units = "degrees_east" ;
        lon:standard_name = "longitude" ;
        lon:axis = "X" ;
        lon:actual_range = -55., -47. ;
    double lat(lat) ;
        lat:long_name = "latitude" ;
        lat:units = "degrees_north" ;
        lat:standard_name = "latitude" ;
        lat:axis = "Y" ;
        lat:actual_range = -24., -10. ;
    float z(lat, lon) ;
        z:long_name = "elevation (m)" ;
        z:_FillValue = NaNf ;
        z:actual_range = 190., 981. ;

// global attributes:
        :Conventions = "CF-1.7" ;
        :title = "Produced by grdcut" ;
        :history = "grdcut @earth_relief_01d_p -R-55/-47/-24/-10 -Gstatic_earth_relief.nc" ;
        :description = "Reduced by Gaussian Cartesian filtering (111.2 km fullwidth) from SRTM15_V2.3.nc [Sandwell et al., 2022; https://doi.org/10.1029/2021EA002069]" ;
        :GMT_version = "6.3.0 [64-bit]" ;
        :node_offset = 1 ;
data:

 lon = -54.5, -53.5, -52.5, -51.5, -50.5, -49.5, -48.5, -47.5 ;

 lat = -23.5, -22.5, -21.5, -20.5, -19.5, -18.5, -17.5, -16.5, -15.5, -14.5, 
    -13.5, -12.5, -11.5, -10.5 ;

 z =
  347.5, 344.5, 386, 640.5, 617, 579, 646.5, 671,
  383, 284.5, 344.5, 394, 491, 556.5, 578.5, 618.5,
  373, 367.5, 349, 352.5, 419.5, 428, 570, 667.5,
  557, 435, 385.5, 345.5, 413.5, 496, 519.5, 833.5,
  561.5, 539, 446.5, 481.5, 439.5, 553, 726.5, 981,
  310, 521.5, 757, 570.5, 538.5, 524, 686.5, 794,
  521.5, 682.5, 796, 886, 571.5, 638.5, 739.5, 881.5,
  308, 595.5, 555.5, 556, 580, 770, 927, 920,
  601, 526.5, 535, 299, 398.5, 645, 797.5, 964,
  494.5, 488.5, 357, 254.5, 286, 484.5, 653.5, 930,
  450.5, 395.5, 366, 248, 250, 354.5, 550, 797.5,
  345.5, 320, 335, 292, 207.5, 247, 325, 346.5,
  349, 313, 325.5, 247, 191, 225, 260, 452.5,
  347.5, 331.5, 309, 282, 190, 208, 299.5, 348 ;
}