ci/etnaviv: Move manual/nightly jobs to postmerge stage

Create a new stage called etnaviv-postmerge and move the full and manual
jobs over there, to avoid entanglement with the pre-merge jobs.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30784>

.gitlab-ci.yml

@@ -159,6 +159,7 @@ stages:
   - freedreno
   - freedreno-postmerge
   - etnaviv
+  - etnaviv-postmerge
   - software-renderer
   - software-renderer-postmerge
   - layered-backends

src/etnaviv/ci/gitlab-ci.yml

@@ -21,7 +21,7 @@
       when: on_success
 
 .etnaviv-manual-rules:
-  stage: etnaviv
+  stage: etnaviv-postmerge
   extends: .no-auto-retry
   rules:
     - !reference [.test, rules]