CA2208 incorrectly issued for C# 14 extension members

### Describe the bug

Use the `nameof` expression on the extension parameter in a C# 14 extension member and CA2208 is emited. It shouldn't be.

### To Reproduce

Try this code:

```csharp
public static class ExampleExtensions
{
extension(IEnumerable sequence)
{
public IEnumerable Sample(int frequency,
[CallerArgumentExpression(nameof(sequence))] string? message = null)
{
if (sequence.Count() < frequency)
throw new ArgumentException($"Expression doesn't have enough elements: {message}", nameof(sequence));
int i = 0;
foreach (T item in sequence)
{
if (i++ % frequency == 0)
yield return item;
}
}
}
}
```

The line that throws a new `ArgumentException` emits CS2208. The explanation is that `sequence` isn't a parameter. But it is, even though it's on the `extension` node.

### Exceptions (if any)

### Further technical details

I reproduced on the VS 2026 G.A. November release.