ci: restore sanity (aka. Revert "ci: don't run sanity in Marge pipelines")

This reverts commit fac60c140b.

Turns out there are pipelines that do not create any other jobs, and
Marge requires a pipeline to pass, which means a pipeline needs to
exist, which means a job needs to always exist.

There is no reason `sanity` would be the one, but it's there so let's
just use it instead of making another one.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26080>

.gitlab-ci.yml

@@ -148,8 +148,6 @@ include:
   - &is-pre-merge '$CI_PIPELINE_SOURCE == "merge_request_event"'
   # Pre-merge pipeline for Marge Bot
   - &is-pre-merge-for-marge '$GITLAB_USER_LOGIN == "marge-bot" && $CI_PIPELINE_SOURCE == "merge_request_event"'
-  # Pre-merge pipeline *not* for Marge Bot
-  - &is-pre-merge-not-for-marge '$GITLAB_USER_LOGIN != "marge-bot" && $CI_PIPELINE_SOURCE == "merge_request_event"'
 
 
 .never-post-merge-rules:
@@ -247,7 +245,7 @@ sanity:
     - .fdo.ci-fairy
   stage: sanity
   rules:
-    - if: *is-pre-merge-not-for-marge
+    - if: *is-pre-merge
       when: on_success
     # Other cases default to never
   variables: