fix: add env.GITHUB_TOKEN to setup-php

[paulbalandan]

Description ~From https://github.com/composer/composer/issues/8710#issuecomment-607710536~

Checklist:

• [x] Securely signed commits
• [ ] Component(s) with PHPDoc blocks, only if necessary or adds value
• [ ] Unit testing, with >80% coverage
• [ ] User guide updated
• [x] Conforms to style guide