Improve wording for vulnerabilities_allowed

What does this MR do and why?

There is a mismatch between the wording and the meaning of vulnerabilities_allowed.

Related issue: #355649 (closed)

Screenshots or screen recordings

Before

After

How to set up and validate locally

1. Enable scan_result_policy feature flag (if you haven't pulled master for a while)
2. Create a security project as described in the docs
3. Create a new scan result policy with the project owner

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.