CI: always save the lockfile.yml in update-repos

The update-repos job can "fail with warnings" if the reference repository
fetch fails. This is intentionally a warning as the CI may have set
KAS_PREMIRRORS and a stale cache is fine.

However, by default artifacts are only saved on successful jobs, so if
this happens the lockfile.yml isn't saved. Ensure the artifacts are
always saved so the rest of the pipeline is successful.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>

.gitlab-ci.yml

@@ -114,6 +114,7 @@ update-repos:
       exit $exit_code
   artifacts:
     name: "lockfile"
+    when: always
     paths:
       - lockfile.yml