support/scripts/generate-gitlab-ci-yml: support scheduled pipelines

Currently the weekly pipelines are triggered from a cron job on the
Buildroot server, so generate-gitlab-ci-yml filters on the "trigger"
source. However, we'd like to schedule it on gitlab itself, which makes
managing it easier.

We could filter on "schedule" in addition to "trigger", but there's not
really a reason to. We can simply rely on the BR_SCHEDULE_JOBS variable
- if it is set, we use its information.

Signed-off-by: Arnout Vandecappelle <arnout@rnout.be>
(cherry picked from commit c0922004d8)
Signed-off-by: Thomas Perale <thomas.perale@mind.be>

support/scripts/generate-gitlab-ci-yml

@@ -42,7 +42,7 @@ gen_tests() {
         do_basics=true
         do_defconfigs=base
         do_runtime=true
-    elif [ "${CI_PIPELINE_SOURCE}" = "trigger" ]; then
+    elif [ -n "${BR_SCHEDULE_JOBS}" ]; then
         case "${BR_SCHEDULE_JOBS}" in
           (basic)
             do_basics=true