chore: pydanticv2 deprecation warning - access model_fields through class (#199)

Signed-off-by: Morgan Epp <60796713+epmog@users.noreply.github.com>

Author: epmog

src/openjd/model/_internal/_create_job.py

@@ -80,7 +80,7 @@ def instantiate_model(  # noqa: C901
         elif create_as_metadata.callable is not None:
             target_model = create_as_metadata.callable(model)
 
-    for field_name in model.model_fields.keys():
+    for field_name in model.__class__.model_fields.keys():
         if field_name in model._job_creation_metadata.exclude_fields:
             # The field is marked for being excluded
             continue