improved type annotations

mvcm/read_data.py

@@ -260,7 +260,7 @@ class ReadData(CollectInputs):
         return rad_data
 
     def preprocess_viirs(
-        self, geo_data: xr.Dataset, viirs: xr.Dataset, hires_data: xr.Dataset = None
+        self, geo_data: xr.Dataset, viirs: xr.Dataset, hires_data: xr.Dataset | None = None
     ) -> xr.Dataset:
         """Create band combinations that are used by some spectral tests.