Detection of duplicate attrset names doesn't work for strings

[dasJ]

Describe the bug

When using strings as attrset values, the duplicate detection doesn't work

Steps to reproduce

Steps to reproduce the behavior:

1. Use this file:

   {
     a = "test";
     a = "test";
   }
   

2. See there are no errors
3. Use this file:

   {
     a = true;
     a = true;
   }
   

4. See the attribute a defined more than once error

Expected behavior

Detection should work no matter the type of the value.

Additional context

• Version of rnix-lsp: unstable-2022-11-27
• Name and version of the editor you've used: nvim 0.9.4
• Operating system: NixOS