dotnet-format will remove `async` from overrided methods which produce IAsyncEnumerable<T> without await, and produce invaild code

dotnet format --version
6.0.252703+68bc36719088c86b0ff01334039b0611741b8276
(from dotnet sdk 6.0.100)

```cs
public abstract class X1
{
public abstract IAsyncEnumerable Test();
}

public class X2 : X1
{
public override async IAsyncEnumerable Test()
{
yield return new object();
}
}
```
`dotnet-format` shouldn't remove `async`, still it will produce invaild code.
And it also shouldn't change the sign of method, since it override an public API.