Based on the issue description and hints provided, I can generate the patch. The `ModelChoiceIteratorValue` class is in `django/forms/widgets.py` and needs a `__hash__` method added. According to the hints from the maintainer, the fix is:

```python
def __hash__(self):
    return hash(self.value)
```

The class likely has an `__eq__` method (since `__eq__` without `__hash__` makes objects unhashable in Python 3), and we need to add the `__hash__` method to make it hashable again.

--- a/django/forms/widgets.py
+++ b/django/forms/widgets.py
@@ -567,6 +567,9 @@ class ModelChoiceIteratorValue:
     def __eq__(self, other):
         if isinstance(other, ModelChoiceIteratorValue):
             other = other.value
         return self.value == other
+
+    def __hash__(self):
+        return hash(self.value)