.github/config/linux-modular.json

{
  "docker_service": "build-linux",
  "on_host_test": true,
  "on_host_test_shards": ["0", "1", "2", "3", "blackbox", "wpt"],
  "platforms": [
    "linux-x64x11-modular"
  ],
  "includes": [
    {
      "name":"modular",
      "platform":"linux-x64x11-modular",
      "target_platform":"linux-x64x11",
      "extra_gn_arguments":"build_with_separate_cobalt_toolchain=true use_contrib_cast=true"
    }
  ]
}