Only exclude PRs with linked issues in the same repo

**What happened**:
On PR https://github.com/anchore/syft/pull/3348 , this is linked to an issue in another repo, which means we'll filter out the PR but we should not have done this since it's an issue that will not be in the issue list.

**What you expected to happen**:
Since we can't find the issue in the same repo we keep the PR as evidence in the changelog

Open question: since this also had `bug` as a label on the PR shouldn't this have been included anyway? That is, shouldn't this have overridden the issue link?

Trace the changelog generator's PR filtering logic using the referenced PR #3348 as the reproduction case. Confirm how linked issues from another repository and the PR's bug label affect inclusion; done means cross-repository issue links do not exclude the PR from the changelog, with the label behavior explicitly settled.

Written by the indexing model from the issue text.