GitLab: Add a default workflow stanza

When validating our current pipeline, a warning is produced about a lack
of a default workflow. For how we use it, we can add a simple default of
"always".

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

.gitlab-ci.yml

@@ -13,6 +13,10 @@ default:
   tags:
     - ${DEFAULT_ALL_TAG}
 
+workflow:
+  rules:
+    - when: always
+
 # Grab our configured image.  The source for this is found
 # in the u-boot tree at tools/docker/Dockerfile
 image: ${MIRROR_DOCKER}/trini/u-boot-gitlab-ci-runner:jammy-20240808-03Dec2024