[syntax-errors] Single starred assignment target (#17024)

Summary
--

Detects starred assignment targets outside of tuples and lists like `*a
= (1,)`.

This PR only considers assignment statements. I also checked annotated
assigment statements, but these give a separate error that we already
catch, so I think they're okay not to consider:

```pycon
>>> *a: list[int] = []
  File "<python-input-72>", line 1
    *a: list[int] = []
      ^
SyntaxError: invalid syntax
```

Fixes #13759

Test Plan
--

New inline tests, plus a new `SemanticSyntaxError` for an existing
parser test. I also removed a now-invalid case from an otherwise-valid
test fixture.

The new semantic error leads to two errors for the case below:

```python
*foo() = 42
```

but this matches [pyright] too.

[pyright]: https://pyright-play.net/?code=FQMw9mAUCUAEC8sAsAmAUEA

crates/ruff_python_parser/resources/valid/statement/assignment.py

@@ -14,8 +14,6 @@ x[y] = (1, 2, 3)
 # This last group of tests checks that assignments we expect to be parsed
 # (including some interesting ones) continue to be parsed successfully.
 
-*foo = 42
-
 [x, y, z] = [1, 2, 3]
 
 (x, y, z) = (1, 2, 3)