Support new GitHub token format

GitHub recently changed their token format: https://github.blog/changelog/2021-03-04-authentication-token-format-updates/

Composer 1.10.1 does not support the new format and it is not possible to create tokens with the old format anymore.
It would be useful to backport this patch: https://github.com/composer/composer/commit/dc83ba93f3d8a35629f9a387632e8cd373a144d0

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: composer 1.10.1-1
ProcVersionSignature: Ubuntu 5.11.0-36.40~20.04.1-generic 5.11.22
Uname: Linux 5.11.0-36-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.20
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: XFCE
Date: Wed Oct 6 14:15:19 2021
InstallationDate: Installed on 2021-02-02 (246 days ago)
InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
PackageArchitecture: all
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=fr_FR.UTF-8
 SHELL=/usr/bin/fish
SourcePackage: composer
UpgradeStatus: No upgrade log present (probably fresh install)