Add @udesou and @qinsoon as CODEOWNERS for gc-* files

[udesou]

Adding @qinsoon and myself to CODEOWNERS so we can get notifications about changes to gc-related files.
It should help us with reviewing minor changes to the Stock GC and also changes that may affect/break the integration with MMTk.

[d-netto]

LGTM, but we might need to double-check if we can we add contributors who have triage bit, but not commit bit, to this file.

[imciner2]

LGTM, but we might need to double-check if we can we add contributors who have triage bit, but not commit bit, to this file.

I think it depends on what the triage permissions are. We recently looked at how to do this in Yggdrasil, where most people don't have any permissions, and we determined that the "Code owners" file is really only good if you have write permissions to the repo, as the GitHub docs state (https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners#codeowners-syntax):

Users and teams must have explicit write access to the repository, even if the team's members already have access.

So it wouldn't work for people who can't write to the repo (and I would assume Triage permissions doesn't include write).