Prevent overwriting type labels from related issue to MR

What does this MR do and why?

This MR prevents overwriting the type::* labels on MRs from related issues if the label is already set on the MR.

This seems to be a bug considering the original MR’s description:

This MR ensures the section/stage/group and type labels from an MR's related issue are applied to the MR (unless such labels are already present).

See also this MR where it kept overwriting the labels:

Expected impact & dry-runs

Action items

• If adding environment variables for reactive processors, update config/triage-web.yaml and .gitlab/ci/triage-web.yml
• (If applicable) Add documentation to the handbook pages for Triage Operations =>
• (If applicable) Identify the affected groups and how to communicate to them:
  • /cc @person_or_group =>
  • Relevant Slack channels =>
  • Engineering week-in-review