View GitHub Artifact storage usage for a given repository. Launch with `<token with repo scope> <owning github user/org name> <repo name>`

ArtifactSizeViewer.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp3.1</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Octokit" Version="0.48.0" />
  </ItemGroup>

</Project>

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Octokit;

namespace ArtifactSizeViewer
{
	class Program
	{
		class ArtifactsPage
		{
			public List<Artifact> Artifacts { get; set; }
		}

		class Artifact
		{
			public long Id { get; set; }

			public string Name { get; set; }

			public long SizeInBytes { get; set; }
		}

		static async Task Main(string[] args)
		{
			var token = args[0];
			var owner = args[1];
			var repo = args[2];

			var client = new GitHubClient(new ProductHeaderValue("ArtifactSizeViewer", "1.0.0"))
			{
				Credentials = new Credentials(token)
			};

			var apiConnection = new ApiConnection(client.Connection);

			var results = await apiConnection.GetAll<ArtifactsPage>(
				new Uri($"repos/{owner}/{repo}/actions/artifacts", UriKind.Relative));

			var totalBytes = results.SelectMany(x => x.Artifacts).Select(x => x.SizeInBytes).Sum();

			var gbUsed = ((double)totalBytes) / 1024 / 1024 / 1024;

			Console.WriteLine($"{gbUsed}GB used.");
		}
	}
}