Maybe Fix Antag Related Crash (#1523)

# Description

I'm trying to fix a crash caused by character profiles saving the same
antag preference twice. I have no clue why or how it's happening, but
this should probably prevent it from happening by making the profile
sanitizer remove duplicate keys before saving them to the database.

The relevant crash log: 

[goobcrash.txt](https://github.com/user-attachments/files/18391763/goobcrash.txt)

# Changelog

:cl:
- fix: Attempted to fix a crash related to antag preferences saving
multiple times.

Co-authored-by: sleepyyapril <[email protected]>

Content.Shared/Preferences/HumanoidCharacterProfile.cs

@@ -478,14 +478,17 @@ public void EnsureValid(ICommonSession session, IDependencyCollection collection
 
         var antags = AntagPreferences
             .Where(id => prototypeManager.TryIndex<AntagPrototype>(id, out var antag) && antag.SetPreference)
+            .Distinct()
             .ToList();
 
         var traits = TraitPreferences
             .Where(prototypeManager.HasIndex<TraitPrototype>)
+            .Distinct()
             .ToList();
 
         var loadouts = LoadoutPreferences
             .Where(l => prototypeManager.HasIndex<LoadoutPrototype>(l.LoadoutName))
+            .Distinct()
             .ToList();
 
         Name = name;