fix WMSWebTile.to_dict() method

[wang-boyu]

There are two web tiles classes with different kind attributes:

@dataclass
class RasterWebTile:
    ...
    kind: str = "raster_web_tile"
    ...

@dataclass
class WMSWebTile(RasterWebTile):
    ...
    kind = "wms_web_tile"
    ...

Apparently WMSWebTile also needs to type-hint its kind field - otherwise it won't get overwritten, as explained here.

This PR fixes this issue.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.18 🎉

Comparison is base (bea0f32) 80.18% compared to head (ea7f389) 80.36%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #140      +/-   ##
==========================================
+ Coverage   80.18%   80.36%   +0.18%     
==========================================
  Files          10       10              
  Lines         656      657       +1     
  Branches      136      136              
==========================================
+ Hits          526      528       +2     
  Misses        114      114              
+ Partials       16       15       -1     

Impacted Files	Coverage Δ
mesa_geo/tile_layers.py	100.00% <100.00%> (ø)
mesa_geo/visualization/modules/MapVisualization.py	91.66% <100.00%> (+1.83%)	⬆️

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[rht]

LGTM