Fix trimming warnings when publishing with Native AOT

[rabuckley]

This fixes the two AOT analysis warnings in this project

IdentityModel.OidcClient/src/OidcClient/Infrastructure/LogSerializer.cs(52): AOT analysis warning IL3050: IdentityModel.OidcClient.Infrastructure.LogSerializer.Serialize(Object): Using member 'System.Text.Json.JsonSerializer.Serialize<Object>(Object,JsonSerializerOptions)' which has 'RequiresDynamicCodeAttribute' can break functionality when AOT compiling. JSON serialization and deserialization might require types that cannot be statically analyzed and might need runtime code generation. Use System.Text.Json source generation for native AOT applications.

IdentityModel.OidcClient/src/OidcClient/Infrastructure/LogSerializer.cs(36): AOT analysis warning IL3050: IdentityModel.OidcClient.Infrastructure.LogSerializer..cctor(): Using member 'System.Text.Json.Serialization.JsonStringEnumConverter.JsonStringEnumConverter()' which has 'RequiresDynamicCodeAttribute' can break functionality when AOT compiling. JsonStringEnumConverter cannot be statically analyzed and requires runtime code generation. Applications should use the generic JsonStringEnumConverter<TEnum> instead.

When targetting net9.0 there are no errors. When targeting net8.0, there is one remaining error, which is tracked in the dotnet runtime by dotnet/runtime#109958.