Update copy in Dependency List popover

Overview

The copy that was approved by Tech Writing (see #353487 (comment 2824008531)) was:

The dependency list excludes vulnerabilities that are no longer detected in the project. Removing these vulnerabilities gives you a more accurate risk assessment of each component.

However, this is what was implemented:

We shouldn't refer to vulnerabilities as "issues" because it gets confusing with issues, GitLab's work item type.