[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/inline/err/single_starred_assignment_target.py

@@ -0,0 +1 @@
+*a = (1,)