feat: authorize composer globally

Sometimes, tests may require own dependencies to be pulled from
authorized packagist endpoint (gitlab.wpdesk.dev), and authorizing only
project-wide is not enough in such cases, leading to missing auth, like
observed in one of CI jobs[^1]

[1]: https://gitlab.wpdesk.dev/wpdesk/heroes/flexible-coupons-shortcodes/-/jobs/1185412#L59



Signed-off-by: Bart Jaskulski <bjaskulski@protonmail.com>