Pass 'TOP_UPSTREAM_SOURCE_SHA' in trigger-build

This is needed because `GITLAB_VERSION` has a special meaning in
`omnibus-gitlab` triggers: this is the GitLab version to build.

The problem is that `omnibus-gitlab` also has triggers to run QA for an
`omnibus-gitlab` commit, and if we use `GITLAB_VERSION` in that case,
the comment would be posted on the GitLab CE/EE commit (stored in
`GITLAB_VERSION`), whci hwouldn't make any sense.
Thus we need `TOP_UPSTREAM_SOURCE_SHA` to represent the commit on
which we want to leave a comment.
Signed-off-by: Rémy Coutable <remy@rymai.me>

scripts/trigger-build

@@ -69,6 +69,7 @@ module Trigger
     def base_variables
       {
         'TOP_UPSTREAM_TRIGGER_PROJECT' => ENV['TOP_UPSTREAM_TRIGGER_PROJECT'] || ENV['CI_PROJECT_PATH'],
+        'TOP_UPSTREAM_SOURCE_SHA' => ENV['CI_COMMIT_SHA'],
         'UPSTREAM_TRIGGER_PROJECT' => ENV['CI_PROJECT_PATH'],
         'UPSTREAM_TRIGGER_SOURCE' => ENV['TRIGGER_SOURCE'],
         'TRIGGERED_USER' => ENV['TRIGGERED_USER'] || ENV['GITLAB_USER_NAME'],