`super()` should not allow attribute assignment

This bug was noticed in pyrefly, and pyright likewise doesn't generate an error in this case.

See [this issue](https://github.com/facebook/pyrefly/issues/251) for details.

Start with the linked pyrefly issue and reproduce the reported `super()` attribute-assignment case in Pyright. Compare the result with the behavior described there and determine what error is expected. Done means Pyright reports the appropriate error for the case, with regression coverage for the discovered behavior.

Written by the indexing model from the issue text.