Fix permission check for confidential quick action

What does this MR do and why?

Checks set_confidentiality instead of admin_issue so that non-members can use the confidential quick action on issue creation.

How to set up and validate locally

1. Create a new issue as a non-member
2. Add /confidential to the description
3. The quick action should take effect

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #276388 (closed)