Fixes error thrown when using multiple files for fields with no time dimension

Author: andrew-s28

parcels/field.py

@@ -686,7 +686,7 @@ def from_netcdf(
         kwargs["data_full_zdim"] = data_full_zdim
 
         if len(data_filenames) > 1 and "time" not in dimensions and timestamps is None:
-            raise RuntimeError("Multiple files given but no time dimension specified")
+            warnings.warn("Multiple files given but no time dimension specified", FieldSetWarning, stacklevel=2)
 
         if grid is None:
             # Concatenate time variable to determine overall dimension