Switch GITLAB_KAS_VERSION to master

What does this MR do?

Switch GITLAB_KAS_VERSION to master, now that release-tools!1265 (comment 451263821) is now merged, and the update_gitlab_kas_version FF is enabled too.

Related issues

https://gitlab.com/gitlab-org/release-tools/-/issues/489

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion

Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• Pipeline is green on dev.gitlab.org if the change is touching anything besides documentation or internal cookbooks - https://dev.gitlab.org/gitlab/omnibus-gitlab/-/merge_requests/199
• trigger-package has a green pipeline running against latest commit

Expected (please provide an explanation if not completing)

• [-] Test plan indicating conditions for success has been posted and passes
• [-] Documentation created/updated
• [-] Tests added
• Integration tests added to GitLab QA, see gitlab!49053 (merged)
• Equivalent MR/issue for the GitLab Chart opened, see gitlab-org/charts/gitlab!1748 (merged)