Fix the DataArray repr in the load_tile_map doctest for xarray v2024.02

[seisman]

xarray v2024.2 was released in Feb, 2024. This new version changed the representation of DataArray (pydata/xarray#8690), making our one doctest failing(https://github.com/GenericMappingTools/pygmt/actions/runs/7982166393/job/21795212745):

_______________ [doctest] pygmt.datasets.tile_map.load_tile_map _______________
115     >>> from pygmt.datasets import load_tile_map
116     >>> raster = load_tile_map(
117     ...     region=[-180.0, 180.0, -90.0, 0.0],  # West, East, South, North
118     ...     zoom=1,  # less detailed zoom level
119     ...     source=contextily.providers.OpenTopoMap,
120     ...     lonlat=True,  # bounding box coordinates are longitude/latitude
121     ... )
122     >>> raster.sizes
123     Frozen({'band': 3, 'y': 256, 'x': 512})
124     >>> raster.coords
Differences (unified diff with -expected +actual):
    @@ -1,4 +1,4 @@
     Coordinates:
    -  * band         (band) uint8 0 1 2
    -  * y            (y) float64 -7.081e-10 -7.858e+04 ... -1.996e+07 ...
    -  * x            (x) float64 -2.004e+07 -1.996e+07 ... 1.996e+07 2.004e+07
    +  * band     (band) uint8 3B 0 1 2
    +  * y        (y) float64 2kB -7.081e-10 -7.858e+04 ... -1.996e+07 -2.004e+07
    +  * x        (x) float64 4kB -2.004e+07 -1.996e+07 ... 1.996e+07 2.004e+07

We can't simply change the output to the new version, because our CI jobs are using different xarray versions (i.e., the minimum supported version with Python 3.10 and the latest version with Python 3.12). We can't make both happy.

We can only let doctest ignore the differences in whitespaces use ellipse for the newly added nbytes.