bug#63141: Incorrect indentation in csharp-mode

[Eli Zaretskii]

> From: Jen-Chieh Shen <jcs090218@gmail.com>
> Date: Fri, 28 Apr 2023 00:25:16 -0700
> 
> It seems like there is an indentation error with the following C# code:
> 
> ```csharp
> public class Foo {
>     [Header("")]
> 
>         [Tooltip("")]
>         [SerializeField]
>         private Block mBlockUp = null;
> }
> ```
> 
> expected behavior:
> 
> ```csharp
> public class Foo {
>     [Header("")]
> 
>     [Tooltip("")]
>     [SerializeField]
>     private Block mBlockUp = null;
> }
> ```
> 
> I've tested this bug with emacs -q, and the bug persists.

Theo, Jostein: could you please take a look?  csharp-ts-mode behaves
correctly with this code snippet, FWIW.  But csharp-mode doesn't.