Github pull request link when pushing branch

This is fairly recent (sept. 2018) and is described as:

When you push a new branch to GitHub from the command line, you’ll now notice a URL within the output which you can copy in order to quickly open a new pull request.

So this is when you are pushing a new branch, not when you are pushing new commits to an existing branch.

I usually just check out a new branch, and then push the new branch up. Get the URL from the message, and use it create a PR for the new branch. Then, I delete the old one (both local, and remote).