swap au/wa/MainRoadsWA WMS source from image/png to image/png32 to improve text legibility (#2675)

Author: andrewharvey

sources/oceania/au/wa/MainRoadsWA-RoadHierarchy.geojson

@@ -15,7 +15,7 @@
             "EPSG:4326",
             "EPSG:4283"
         ],
-        "url": "https://gisservices.mainroads.wa.gov.au/arcgis/services/OpenData/RoadAssets_DataPortal/MapServer/WMSServer?request=GetMap&service=WMS&format=image/png&transparent=TRUE&version=1.3.0&layers=15&styles=&crs={proj}&width={width}&height={height}&bbox={bbox}",
+        "url": "https://gisservices.mainroads.wa.gov.au/arcgis/services/OpenData/RoadAssets_DataPortal/MapServer/WMSServer?request=GetMap&service=WMS&format=image/png32&transparent=TRUE&version=1.3.0&layers=15&styles=&crs={proj}&width={width}&height={height}&bbox={bbox}",
         "overlay": true,
         "max_zoom": 21,
         "country_code": "AU",