ci: Add "is pre-merge pipeline" YAML anchor

Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6566>
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 729a1f4..c4cc688 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -59,6 +59,9 @@
     # Post-merge pipeline, not for Marge Bot
     - if: &is-post-merge-not-for-marge '$GITLAB_USER_LOGIN != "marge-bot" && $CI_MERGE_REQUEST_SOURCE_BRANCH_NAME != $CI_COMMIT_REF_NAME && $CI_PROJECT_PATH == "mesa/mesa"'
       when: on_success
+    # Pre-merge pipeline
+    - if: &is-pre-merge '$CI_MERGE_REQUEST_SOURCE_BRANCH_NAME == $CI_COMMIT_REF_NAME'
+      when: on_success
     # Pre-merge pipeline for Marge Bot
     - if: &is-pre-merge-for-marge '$GITLAB_USER_LOGIN == "marge-bot" && $CI_MERGE_REQUEST_SOURCE_BRANCH_NAME == $CI_COMMIT_REF_NAME'
       when: on_success
@@ -151,7 +154,7 @@
       when: never
     - changes: *all_paths
       when: never
-    - if: '$CI_MERGE_REQUEST_SOURCE_BRANCH_NAME == $CI_COMMIT_REF_NAME'
+    - if: *is-pre-merge
       when: on_success
   variables:
     GIT_STRATEGY: none