chore(ci): update workflow runs-on label to ubuntu-latest

.gitea/workflows/snapshot_admin.yml

@@ -17,7 +17,7 @@ jobs:
   # Push-only smoke gate: no deployment, no web UI smoke, no long-running side effects.
   validate-snapshot-admin-smoke:
     if: github.event_name == 'push'
-    runs-on: self-hosted
+    runs-on: ubuntu-latest
     steps:
       - name: Checkout Code
         run: |
@@ -53,7 +53,7 @@ jobs:
   # Manual dispatch gate: full workflow + web UI validation only.
   validate-snapshot-admin-full:
     if: github.event_name == 'workflow_dispatch'
-    runs-on: self-hosted
+    runs-on: ubuntu-latest
     steps:
       - name: Checkout Code
         run: |