Broken links to MRs in changelog

Summary

Looking at the changelog, the links to issues/MR from towncrier are broken.

I think that:

issue_format = "`!{issue} <https://gitlab.cta-observatory.org/cta-computing/dpps/aiv/test-report/-/merge_requests/{issue}>`__"

should be instead:

issue_format = "`!{issue} <https://gitlab.cta-observatory.org/cta-computing/dpps/aiv/dpps-aiv-toolkit/-/merge_requests/{issue}>`__"