Fix admin welcome illustration not found

ee/app/views/dashboard/projects/_blank_state_ee_trial.html.haml

 .blank-state
   .blank-state-icon
-    = image_tag("illustrations/lock_promotion")
+    = image_tag("illustrations/lock_promotion.svg", { lazy: false })
   .blank-state-body
     %h3.blank-state-title
       Unlock more features with GitLab Ultimate

ee/changelogs/unreleased/34768-fix-welcome-images-for-admin.yml

+---
+title: Fix admin welcome image not found
+merge_request: 19676
+author:
+type: fixed