fix(centpkg): deduce the GitLab token from the vars

After switching to templated authentication methods for git forges
instead of using the hard-coded values in `extra-vars.yml`, I forgot to
adjust this one place where we utilize the GitLab token too.

Signed-off-by: Matej Focko <[email protected]>

Author: mfocko

secrets/packit/prod/centpkg-sig.conf.j2

@@ -29,4 +29,6 @@ git_excludes =
 
 [centpkg-sig.distgit]
 apibaseurl = https://gitlab.com
-token = {{ vault.packit_service.authentication['gitlab.com'].token }}
+{% set gitlab_forge = git_forges | selectattr('name', 'equalto', 'gitlab.com') | first %}
+{% set gitlab_fields = gitlab_forge['fields'] | items2dict(key_name='name') %}
+token = {{ gitlab_fields['token:key'] }}

secrets/packit/stg/centpkg-sig.conf.j2

@@ -29,4 +29,6 @@ git_excludes =
 
 [centpkg-sig.distgit]
 apibaseurl = https://gitlab.com
-token = {{ vault.packit_service.authentication['gitlab.com'].token }}
+{% set gitlab_forge = git_forges | selectattr('name', 'equalto', 'gitlab.com') | first %}
+{% set gitlab_fields = gitlab_forge['fields'] | items2dict(key_name='name') %}
+token = {{ gitlab_fields['token:key'] }}