[github/add-branch-to-gh-pr-checkout] Do not hardcode `me`

[Kocal]

In

userScripts/scripts/github/add-branch-to-gh-pr-checkout.user.js

Line 18 in bc276ca

const me = 'kocal';

Get author from <meta name="user-login" content="Kocal"> instead of hardcoding it