ci: gate e2e job on fast-gate success

Resolve the audit blocker: the e2e (container) job must not run when the
fast gate failed. It stays independent of the preview build -- when the
amd64 digest is missing it falls back to a local build for forks, merge
groups and validate dispatches.

.github/workflows/ci.yml

@@ -107,7 +107,7 @@ jobs:
     name: Container and E2E
     needs: [fast-gate, preview-amd64]
     if: |
-      !cancelled() &&
+      !cancelled() && needs.fast-gate.result == 'success' &&
       (
         github.event_name == 'merge_group' ||
         (github.event_name == 'push' && github.ref == 'refs/heads/release/v2') ||