Fix inconsistent jobs ordering when using parallel >= 10"

What does this MR do and why?

This change fixes how parallel jobs are sorted in the pipeline minigraph on the MR page. Previously, jobs with names like "test 1/10", "test 2/10", "test 10/10" were being sorted alphabetically, which would put "test 10/10" before "test 2/10". Now they sort numerically using the existing sortable_name method, so they appear in the correct order: 1, 2, 10, 20, etc.

This is the same approach used by Ci::Group.fabricate.

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Create an MR with the following .gitlab-ci.yml config:

stages:
  - test

FastTest:
  stage: test
  parallel: 10
  script:
    - echo "Running FastTest $CI_NODE_INDEX of $CI_NODE_TOTAL"
    - sleep 5
 

2. Open the MR and select the Pipelines tab.
3. Select a stage and verify the jobs are correctly ordered.

MR acceptance checklist

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Related to #414452 (closed)