Fix doctest on pygmt.datasets.tile_map.load_tile_map in ci_tests_legacy

[weiji14]

Description of proposed changes

Fix doctest failure on ci_tests_legacy.yaml caused by the changes made in #3575/#3576 that made it incompatible with older versions of rasterio<1.4.2

_______________ [doctest] pygmt.datasets.tile_map.load_tile_map ________________
118     >>> raster.sizes
119     Frozen({'band': 3, 'y': 256, 'x': 512})
120     >>> raster.coords  # doctest: +ELLIPSIS, +NORMALIZE_WHITESPACE
121     Coordinates:
122       * band         (band) uint8... 1 2 3
123       * y            (y) float64... -7.081e-10 -7.858e+04 ... -1.996e+07 -2.004e+07
124       * x            (x) float64... -2.004e+07 -1.996e+07 ... 1.996e+07 2.004e+07
125         spatial_ref  int... 0
126     >>> # CRS is set only if rioxarray is available
127     >>> if hasattr(raster, "rio"):
Expected:
    CRS.from_wkt(...)
Got:
    CRS.from_epsg(3857)
/home/runner/work/pygmt/pygmt/pygmt/datasets/tile_map.py:127: DocTestFailure

Fixes ##3641 (comment), patches #3576

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