fix: raise AttributeError instead of returning None on __getattr__.

The __getattr__ method should always raise an AttributeError if the value does not exist instead of returning None. The existing implementation causes issues when converting to a Pandas DataFrame

src/posit/connect/resources.py

@@ -40,7 +40,7 @@ def __getattr__(self, name):
                 stacklevel=2,
             )
             return self[name]
-        return None
+        raise AttributeError(f"'{self.__class__.__name__}' object has no attribute '{name}'")
 
     def update(self, *args, **kwargs):
         super().update(*args, **kwargs)