Fix broken unit test caused by non-existent model path.

invokeai/backend/model_manager/probe.py

@@ -256,6 +256,12 @@ class ModelProbe(object):
             return ModelType.SpandrelImageToImage
         except spandrel.UnsupportedModelError:
             pass
+        except RuntimeError as e:
+            if "No such file or directory" in str(e):
+                # This error is expected if the model_path does not exist (which is the case in some unit tests).
+                pass
+            else:
+                raise e
 
         raise InvalidModelConfigException(f"Unable to determine model type for {model_path}")