[Token notifications] Clarify owners are also notified of PAT expiry

What does this MR do?

• This customer had identified an ambiguity in our description of who receives notifications of upcoming Project Access Token expiries
• The existing text only mentions maintainers, while members with the owner role will also receive a notification (as clarified in this comment).
• Assigning review to @rdickenson as you are listed as the TW for Security - please redirect me if I should assign review to somebody else 👍

Related issues

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