How to merge on your machine?
git fetch origin refs/mr/rg_xxxxxxxx:local_branch
git checkout master
git merge local_branch
How to "see" all pull requests as branches:
Add, in config file (.git/config), under the remote you want, a line like this:
fetch = +refs/pr/*:refs/remotes/your_remote_name_for_example_origin/mr/*
After you run a git fetch, you will have all the pull requests locally.
For example, you can merge one of them:
git checkout master
git merge pr/xxxxxxxx