adapt to KernelParameter API changes

src/pystencilssfg/ir/source_components.py

@@ -168,7 +168,7 @@ class SfgKernelHandle:
 
         for param in self._parameters:
             if param.wrapped.is_field_parameter:
-                self._fields |= param.wrapped.fields
+                self._fields |= set(param.wrapped.fields)
             else:
                 self._scalar_params.add(param)