NpgsqlDbContextOptionsBuilder.MapEnum<T> doesn't respect PgNameAttribute

[zotanmew]

As discussed in #3178, here's a minimal repro (untested, but using the same patterns as our big application, if it doesn't work I'll create a full repo and link it here):

builder.Services.AddNpgsql<DatabaseContext>("<connectionString>", opts =>
{
	opts.ConfigureDataSource(dataSource => { dataSource.MapEnum<Example.ExampleEnum>(); });
	opts.MapEnum<Example.ExampleEnum>();
});

alongside

class DatabaseContext(DbContextOptions<DatabaseContext> options) : DbContext(options)
{
	public virtual DbSet<Example> Examples { get; init; } = null!;
}

public class Example
{
	[PgName("example_enum")]
	public enum ExampleEnum
	{
		Test,
		OtherTest
	}

	public ExampleEnum ExampleValue { get; set; }
}

When used in a query, causes an exception containing MessageText: type "example" does not exist.

When leaving out either of the MapEnum<T> calls, an InvalidCastException is thrown on query.