[Pull Requests] Fix Symfony upstream URL as git:// isn't supported by Github anymore.

[alexandre-daubois]

See: https://github.blog/2021-09-01-improving-git-protocol-security-github/
It is impossible to fetch anything now with the git:// URL.

symfony$ git fetch upstream
fatal: erreur distante : 
  The unauthenticated git protocol on port 9418 is no longer supported.
Please see https://github.blog/2021-09-01-improving-git-protocol-security-github/ for more information.

[javiereguiluz]

Good catch, thanks Alexandre.

[alexislefebvre]

Why not use git@github.com which is already used to clone the fork? (code is shown before this code)

[alexandre-daubois]

@alexislefebvre I'd say git@github.com uses SSH. HTTPS URL doesn't, which seems more convenient.

[alexislefebvre]

git clone already uses git@github.com, so it should work at this point.

I think it would be more consistent to use git@github.com on both commands: https://symfony.com/doc/current/contributing/code/pull_requests.html#get-the-symfony-source-code

This will be equally convenient, if git@github.com works for git clone, it should work for git remote too, or am I missing something?