Merge branch 'sh-revert-mr-22911' into 'master'

Revert "Merge branch '28682-can-merge-branch-before-build-is-started' into 'master'"

See merge request gitlab-org/gitlab-ce!23715

app/models/merge_request.rb

@@ -978,6 +978,7 @@ class MergeRequest < ActiveRecord::Base
 
   def mergeable_ci_state?
     return true unless project.only_allow_merge_if_pipeline_succeeds?
+    return true unless head_pipeline
 
     actual_head_pipeline&.success? || actual_head_pipeline&.skipped?
   end

changelogs/unreleased/28682-can-merge-branch-before-build-is-started.yml

----
-title: Strictly require a pipeline to merge.
-merge_request: 22911
-author:
-type: changed

spec/models/merge_request_spec.rb

@@ -1885,7 +1885,7 @@ describe MergeRequest do
           allow(subject).to receive(:head_pipeline) { nil }
         end
 
-        it { expect(subject.mergeable_ci_state?).to be_falsey }
+        it { expect(subject.mergeable_ci_state?).to be_truthy }
       end
     end