Make sure all pipelines would go to pending once

Without this fix, pipeline could go from skipped to
running directly, bypassing the transition for:

    [:created, :pending] => :running

And this is responsible for setting up started_at.
Without this fix, started_at would never be set.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/39884

app/models/ci/pipeline.rb

@@ -66,8 +66,8 @@ module Ci
 
     state_machine :status, initial: :created do
       event :enqueue do
-        transition created: :pending
-        transition [:success, :failed, :canceled, :skipped] => :running
+        transition [:created, :skipped] => :pending
+        transition [:success, :failed, :canceled] => :running
       end
 
       event :run do

changelogs/unreleased/39884-fix-pipeline-transition-with-single-manual-action.yml

@@ -0,0 +1,6 @@
+---
+title: Fix pipeline status transition for single manual job. This would also fix pipeline
+  duration becuse it is depending on status transition
+merge_request: 15251
+author:
+type: fixed

spec/services/ci/process_pipeline_service_spec.rb

@@ -292,6 +292,30 @@ describe Ci::ProcessPipelineService, '#execute' do
     end
   end
 
+  context 'when there is only one manual action' do
+    before do
+      create_build('deploy', stage_idx: 0, when: 'manual', allow_failure: true)
+
+      process_pipeline
+    end
+
+    it 'skips the pipeline' do
+      expect(pipeline.reload).to be_skipped
+    end
+
+    context 'when the action was played' do
+      before do
+        play_manual_action('deploy')
+      end
+
+      it 'queues the action and pipeline' do
+        expect(all_builds_statuses).to eq(%w[pending])
+
+        expect(pipeline.reload).to be_pending
+      end
+    end
+  end
+
   context 'when blocking manual actions are defined' do
     before do
       create_build('code:test', stage_idx: 0)