Remove stale CODEOWNERS entries: corey-oas and gbowen1

Why is this change being made?

Two stale code owners are removed from .gitlab/CODEOWNERS. Being listed there after departure means merge requests touching those pages request review from an account that can never approve, which silently blocks the approval path.

1. @corey-oas — restoring a reverted removal

MR 20561 removed @corey-oas from CODEOWNERS on 2026-07-24, as he has left GitLab.

MR 20565 then partially reverted that removal. It was branched before MR 20561 merged, so its copy of .gitlab/CODEOWNERS still contained the old line, and on merge that stale line won — putting @corey-oas back as a code owner of /content/handbook/security/isms.md.

Scope of the regression: MR 20561 removed @corey-oas from 11 lines. Only the isms.md line came back, because that was the only one adjacent to a hunk MR 20565 also edited. The other 10 removals are intact, and no other change from MR 20561 was affected.

-/content/handbook/security/isms.md @corey-oas @cynthiamiller @gitlab-com/egroup @gitlab-com/content-sites @bill_staples @cmazal
+/content/handbook/security/isms.md @cynthiamiller @gitlab-com/egroup @gitlab-com/content-sites @bill_staples @cmazal

2. @gbowen1 — removing a stale code owner

@gbowen1 is removed as a code owner from the four CorpSec systems paths that listed him:

1. /content/handbook/security/corporate/systems/okta/
2. /content/handbook/security/corporate/systems/google/
3. /content/handbook/security/corporate/systems/lumos/
4. /content/handbook/security/corporate/systems/slack/

Each line retains @gitlab-com/gl-security/corp/identity plus the other named owners, so all four paths keep full CODEOWNERS coverage.

After this change both @corey-oas and @gbowen1 appear zero times in CODEOWNERS. No other file is touched.

Author and Reviewer Checklist

Please verify the check list and ensure to tick them off before the MR is merged.

• Provided a concise title for this Merge Request (MR)
• Added a description to this MR explaining the reasons for the proposed change, per say why, not just what
• Assign reviewers for this MR to the correct
  • The when to get approval handbook section explains when DRI approval is required
  • The who can approve handbook section explains how to identify the DRI
  • If the MR does not require DRI approval, consider asking someone on your team, such as your manager.
  • The approver may merge the MR. If they approve but don't merge, you can merge.
• For transparency, share this MR with the audience that will be impacted.
  • Team: For changes that affect your direct team, share in your group Slack channel
  • Department: If the update affects your department, share the MR in your department Slack channel
  • Division: If the update affects your division, share the MR in your division Slack channel
  • Company: If the update affects all (or the majority of) GitLab team members, post an update in #whats-happening-at-gitlab linking to this MR

Commits

• 83854dad Remove gbowen1 from CODEOWNERS
• fd3c0573 Restore corey-oas removal from CODEOWNERS

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