If fetching upstream requires opening a pull request so that conflicts can be resolved, and such conflicts are resolved as follows, then a merge is completed without letting CI run.
This is a specific example of what Github recommends for resolving conflicts using command line.
git checkout -b mastodon-main main
git pull https://github.com/mastodon/mastodon.git main
git o mastodon-main
Then commit to finish merge... (don't do this)
git o main
git merge --no-ff mastodon-main
git push origin main