SyntaxWarning: "is not" with a string literal

The current code produces the following syntax warning when run under python 3.11:

```
/opt/ncid/api.py:138: SyntaxWarning: "is not" with a literal. Did you mean "!="?
  visible_models = [model for model in list(models.keys()) if model is not "Rotor-SVM"]
```