bloom says "Cannot push to remote release repository"

edit

I got this error when I ran bloom-release with a metapackage that I joined maintainer team after it's been already released. Am I missing anything?

----error msg----
$ bloom-release pkg_a groovy
==> Fetching 'pkg_a' repository from
'https://github.com/ros-gbp/pkg_a-release.git'
==> Testing for push permission on release repository
Username for 'https://github.com': my_github_account
Password for 'https://my_github_account@github.com':
error: The requested URL returned error: 403 Forbidden while accessing
https://github.com/ros-gbp/pkg_a-release.git/info/refs
fatal: HTTP request failed
Cannot push to remote release repository.

I suspect I don't have a push privilege to the release repository (but tutorials of bloom didn't tell me to ask for a push access).