Reword the vulnerability resolution alert title

What does this MR do and why?

On the vulnerability details page, the resolution alert said Vulnerability resolved in <branch> while the status badge next to it could still say Needs triage. Resolved is also one of the workflow statuses, so the title read as if no further action was needed.

This rewords the alert title in resolution_alert.vue, as proposed in #599426 (closed):

• Vulnerability resolved in <branch> → No longer detected in <branch>
• Vulnerability resolved in the default branch → No longer detected in the default branch

The new title matches:

• the alert body, which already says the vulnerability is no longer detected and asks the user to verify before changing its status;
• the vulnerability docs, which say "no longer detected in the default branch";
• the vulnerability_no_longer_detected_on_default_branch internal event, and the resolution_badge.vue tooltip, which already avoids the word "resolved".

I used "in" rather than the issue's "on" to match the docs. The status badge, the alert body and the dismiss behavior are unchanged. The strings move to the Vulnerability| namespace used by the other components in this directory.

References

• Closes #599426 (closed)

Screenshots or screen recordings

Before	After
Vulnerability resolved in main	No longer detected in main
Vulnerability resolved in the default branch	No longer detected in the default branch

The alert body is unchanged: The vulnerability is no longer detected. Verify the vulnerability has been remediated before changing its status.

How to set up and validate locally

1. In a project with security scanning, open a vulnerability that is no longer detected on the default branch.
2. The alert at the top of the page is titled No longer detected in <default branch>, and the status badge still shows the workflow status, for example Needs triage.

Specs: yarn jest ee/spec/frontend/vulnerabilities/resolution_alert_spec.js

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