[syntax-errors] Limit `except*` range to `*` (#16473)
Summary
--
This is a follow-up to #16446 to fix the diagnostic range to point to
the `*` like `pyright` does
(https://github.com/astral-sh/ruff/pull/16446#discussion_r1976900643).
Storing the range in the `ExceptClauseKind::Star` variant feels slightly
awkward, but we don't store the star itself anywhere on the
`ExceptHandler`. And we can't just take `ExceptHandler.start() +
"except".text_len()` because this code appears to be valid:
```python
try: ...
except * Error: ...
```
Test Plan
--
Existing tests.
