venus/ci: make sure nightly job doesn't get retried

It's long enough as it is, we don't want to waste 2x the resources when
a test fails.

Fixes: 0db4bb2ea0 ("venus/ci: add manual/nightly venus-lavapipe-full")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29844>

src/virtio/ci/gitlab-ci-inc.yml

@@ -9,6 +9,7 @@
 
 .venus-manual-rules:
   stage: layered-backends
+  retry: !reference [.scheduled_pipeline-rules, retry]
   rules:
     - !reference [.test, rules]
     - !reference [.lavapipe-manual-rules, rules]