If you use GitHub issues, you can close them by adding a text like
closes #1 to the commit message to close them. You can use other keywords than
closes to do that. You can use any of the following:
Note: This seems to work in GitLab too!
You can even close issues in another repository, assuming that you have push access to that. The syntax is the
<repo-owner-name>/<repo-name>#<repo-id>, so an example would be