ci/anv: Make anv-manual-rules actually manual on anv-only changes.

I guess that's why I've seen some zink-anv-tgl-full runs (the only
consumer) happen on people's MRs that I hadn't kicked off myself.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20163>

.gitlab-ci/test-source-dep.yml

@@ -896,7 +896,7 @@
     - !reference [.vulkan-manual-rules, rules]
     - changes:
       - src/intel/**/*
-      when: on_success
+      when: manual
 
 .hasvk-rules:
   stage: intel