git checkout new-feature # Go to the feature branch named "new-feature"
git rebase master
# Now your feature have all the commits from master!
# this is because "git rebase master" reads like "git, please rebase my commits on top on the commits from master"
git checkout master # Go back to master
git merge --ff-only new-feature
(see https://shinglyu.com/web/2018/03/25/merge-pull-requests-without-merge-commits.html)