[tracker/wip/carlosg/ci-pipelines: 4/7] ci: Enable detached merge request pipelines

[Carlos Garnacho <carlosg src gnome org>]

commit b614278e6cd169ab705080010f22f36a910c31c0
Author: Carlos Garnacho <carlosg gnome org>
Date:   Sat Feb 19 10:54:39 2022 +0100

    ci: Enable detached merge request pipelines
    
    The check jobs are relying on environment variables that are only
    set on merge request pipelines, so they've been kinda ineffective
    so far.
    
    Enable the detached merge request pipelines as documented at
    https://docs.gitlab.com/ee/ci/pipelines/merge_request_pipelines.html
    so that these work. Since we want all jobs to run in merge pipelines,
    using "workflow" is good for us.

 .gitlab-ci.yml | 5 +++++
 1 file changed, 5 insertions(+)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 2b6f55c48..908fe3aad 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -23,6 +23,11 @@ stages:
   - analysis
   - website
 
+workflow:
+  rules:
+    - if: $CI_PIPELINE_SOURCE == 'merge_request_event'
+    - if: $CI_PIPELINE_SOURCE == 'push'
+
 .check-template: &check
   extends:
     - .fdo.ci-fairy