We were alerted to this issue after we already fixed it by refactoring that part of Yoast SEO. As a result, there was no specific pull request to resolve this particular issue.
And as a result of that, when going over the commits to create the changelog, we missed that we fixed this issue in the process.
We’ll keep an extra eye out for situations like this in the future, so that security fixes are always in the changelog.
TL;DR: it should have been in the changelog, but we missed that we’d resolved it when writing the changelog. In the future, all (security) fixes will be listed.