Fix rendering of stream form fields (#3622)

How to reproduce:
- open a application submisssion with checkboxes as an form element.
- Get the error below

```
'str' object has no attribute 'help_text'
```

hypha/apply/categories/blocks.py

@@ -92,7 +92,7 @@ def render(self, value, context):
         for field in category_fields.keys():
             if not value.get(field):
                 category = value["category"]
-                if isinstance(category, int):
+                if isinstance(category, int) or isinstance(category, str):
                     category = self.get_instance(id=category)
                 value[field] = getattr(category, category_fields[field])
         return super().render(value, context)