async functions always finish on a background thread

internal static async Task GenerateChunkAsync(Dictionary<Vector3Int, Chunk> chunks)
{
    // Any main-thread setup here

    var chunkData = await Task.Run(() =>
    {
        // Execute code on a background thread
        var data = SomeFunc(5);
        return data;
    });

    // Finish running on the main thread (important for opengl)
    // For some reason, this always runs on the background thread that the Task.Run code was running on
    Console.WriteLine($"Finished function in {chunkData}ms. Is main thread: {Engine.IsMainThread}");
}

private static long SomeFunc(int sleepTime)
{
    var timer = new System.Diagnostics.Stopwatch();
    timer.Start();
    
    // Simulate some background work
    Thread.Sleep(sleepTime * 1000);
    
    timer.Stop();
    return timer.ElapsedMilliseconds;
}