hydra-eval-jobs is unnecessarily dropping jobs with "." in their name

[JulienMalka]

Describe the bug Hydra is unnecessarily dropping jobs that have a "." in their name. See here in the code of hydra-eval-jobs: https://github.com/NixOS/hydra/blob/082495e34e094cae1eb49dbfc5648938e23c6355/src/hydra-eval-jobs/hydra-eval-jobs.cc#L246-L250

I've computed that this bug currently induces a drop of 136 jobs in the nixpkgs/trunk jobset.

To Reproduce

The bug can be reproduced by evaluating this flake with hydra-eval-jobs:

{
  description = "A debugging flake";

  outputs = { self }:

    let
      sample = derivation { name = "sample"; builder = "sample"; system = "mysystem"; };
    in
    {
      hydraJobs = {
        "a.b" = sample;
        a.b = sample;
      };
    };
}