To avoid self-hosting a full-fledged code forge, you might want to simply store issues in the git repo itself. Have you tried using git-bug, git-issue, or some other decentralized bug tracker?
* https://github.com/git-bug/git-bug
* https://github.com/dspinellis/git-issue
Last time I tried git-bug I failed to import my issues from GitHub and gave up, but maybe it works now, it seems there is a new & more active maintainer.