Hello!
I would like to report that using [IterationSetup] is causing 400B to be allocated.
I quickly checked how it works for earlier versions and it seems that the problem started in 0.13.6 and persists in 0.13.12.

Please check the summary and code below:

BenchmarkDotNet v0.13.12, Windows 10 (10.0.19045.4529/22H2/2022Update)
11th Gen Intel Core i7-1185G7 3.00GHz, 1 CPU, 8 logical and 4 physical cores
.NET SDK 8.0.106
[Host] : .NET 8.0.6 (8.0.624.26715), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI
Job-HVPPIJ : .NET 8.0.6 (8.0.624.26715), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI

InvocationCount=1 UnrollFactor=1

Method	Mean	Error	Allocated
TestBenchmark	0.0 ns	0.0 ns	400 B

using BenchmarkDotNet.Attributes;

BenchmarkDotNet.Running.BenchmarkRunner.Run<Test>();

[MemoryDiagnoser]
public class Test
{
    [IterationSetup]
    public void TestSetup()
    {
    }

    [Benchmark]
    public void TestBenchmark()
    {
    }
}

If I remove IterationSetup or change it to GlobalSetup, the problem does not occur.

BenchmarkDotNet v0.13.12, Windows 10 (10.0.19045.4529/22H2/2022Update)
11th Gen Intel Core i7-1185G7 3.00GHz, 1 CPU, 8 logical and 4 physical cores
.NET SDK 8.0.106
[Host] : .NET 8.0.6 (8.0.624.26715), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI
DefaultJob : .NET 8.0.6 (8.0.624.26715), X64 RyuJIT AVX-512F+CD+BW+DQ+VL+VBMI

Method	Mean	Error	StdDev	Allocated
TestBenchmark	0.0698 ns	0.0279 ns	0.0466 ns	-

Thanks!