Fix WebAuthn not working after move to System.Text.Json (#1818)

src/Core/Entities/User.cs

@@ -132,6 +132,7 @@ namespace Bit.Core.Entities
 
         public void SetTwoFactorProviders(Dictionary<TwoFactorProviderType, TwoFactorProvider> providers)
         {
+            // When replacing with system.text remember to remove the extra serialization in WebAuthnTokenProvider.
             TwoFactorProviders = JsonHelpers.LegacySerialize(providers);
             _twoFactorProviders = providers;
         }