HideColumns + custom corerun = incorrect table markdown

[EgorBo]

Minimal repro:

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).Run(args);

[HideColumns("Job", "StdDev", "RatioSD")]
public class MyBench
{
    [Benchmark]
    public bool Test() => true;
}

If I run this benchmark with a custom corerun, e.g.:

dotnet run -c Release -- --filter "*" --coreRun Path\to\corerun.exe

it outputs this:

| Method | Mean      | Error     |
|------- |----------:|----------:|-
| Test   | 0.0062 ns | 0.0042 ns |

that trailing |- on the 2nd row makes the whole markdown invalid, e.g. here is what happens if I paste it here:

| Method | Mean | Error |
|------- |----------:|----------:|-
| Test | 0.0062 ns | 0.0042 ns |

While it should be:

Method	Mean	Error
Test	0.0062 ns	0.0042 ns

I can try to fix it myself unless you know that it can be trivially fixed 🙂

[adamsitnik]

cc @YegorStepanov who contributed this feature in #1890

[timcassell]

Possibly introduced in #2410. cc @Vahdanian