ci: Only run by default when scheduled for merge request

VirGL just runs way too many jobs, with each pipeline consuming the
entire committed x86-64 build capacity we have available, so we need to
restrict it anyway. This is made worse by the fact it will create
duplicate pipelines for merge requests.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Part-of: <https://gitlab.freedesktop.org/virgl/virglrenderer/-/merge_requests/744>

.gitlab-ci.yml

@@ -32,6 +32,38 @@ include:
     file:
       - '/.gitlab-ci/image-tags.yml'
 
+# YAML anchors for rule conditions
+# --------------------------------
+.rules-anchors:
+  rules:
+    # Scheduled pipeline
+    - if: &is-scheduled-pipeline '$CI_PIPELINE_SOURCE == "schedule"'
+      when: on_success
+    # For Marge Bot
+    - if: &is-for-marge '$GITLAB_USER_LOGIN == "marge-bot"'
+      when: never
+    # Forked project branch
+    - if: &is-forked-branch '$CI_PROJECT_NAMESPACE != "virgl" && $CI_MERGE_REQUEST_SOURCE_BRANCH_NAME != $CI_COMMIT_REF_NAME'
+      when: manual
+    # Forked project branch / pre-merge pipeline not for Marge bot
+    - if: &is-forked-branch-or-pre-merge-not-for-marge '$CI_PROJECT_NAMESPACE != "virgl" || ($GITLAB_USER_LOGIN != "marge-bot" && $CI_MERGE_REQUEST_SOURCE_BRANCH_NAME == $CI_COMMIT_REF_NAME)'
+      when: manual
+    # Pipeline runs for the main branch of the upstream virglrenderer project
+    - if: &is-virglrenderer-main '$CI_PROJECT_NAMESPACE == "virgl" && $CI_COMMIT_REF_NAME == $CI_DEFAULT_BRANCH && $CI_MERGE_REQUEST_SOURCE_BRANCH_NAME != $CI_DEFAULT_BRANCH'
+      when: always
+    # Post-merge pipeline
+    - if: &is-post-merge '$CI_PROJECT_NAMESPACE == "virgl" && $CI_MERGE_REQUEST_SOURCE_BRANCH_NAME != $CI_COMMIT_REF_NAME'
+      when: on_success
+    # Post-merge pipeline, not for Marge Bot
+    - if: &is-post-merge-not-for-marge '$CI_PROJECT_NAMESPACE == "virgl" && $GITLAB_USER_LOGIN != "marge-bot" && $CI_MERGE_REQUEST_SOURCE_BRANCH_NAME != $CI_COMMIT_REF_NAME'
+      when: on_success
+    # Pre-merge pipeline
+    - if: &is-pre-merge '$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
+
 stages:
   - build
   - sanity test
@@ -64,11 +96,16 @@ debian/x86_build:
     paths:
       - install/
       - results/
-  only:
-    - branches
-    - tags
-    - merge_requests
-    - schedules
+  rules:
+    - if: *is-scheduled-pipeline
+      when: on_success
+    - if: *is-post-merge
+      when: never
+    - if: *is-forked-branch-or-pre-merge-not-for-marge
+      when: manual
+    - if: *is-pre-merge-for-marge
+      when: on_success
+    - when: manual
 
 #
 # Sanity test jobs
@@ -77,6 +114,7 @@ debian/x86_build:
 .make_check_base:
   stage: sanity test
   extends: debian/x86_build
+  dependencies: []
   artifacts:
     when: always
     paths:
@@ -126,13 +164,10 @@ make check venus:
       - results/
     reports:
       junit: results/junit.xml
-  needs:
+  dependencies:
     - debian/x86_build
-  only:
-    - branches
-    - tags
-    - merge_requests
-    - schedules
+  rules:
+    - when: on_success
 
 .gl-host-test:
   extends: