Fix calculation of used extra CI minutes

When a Group/Personal namespace is using the Free plan on GL.com then
the assigned CI minutes is read from
`Gitlab::CurrentSettings.shared_runners_minutes` and not from
`Namespace#shared_runners_minutes`.

In the previous version we were using
`Namespace#shared_runners_minutes_limit` which was returning `nil`
instead of 2000 (The current default CI minutes configured globally for
free plans in GL.com). This bug was affecting Pipelines and was showing
wrong information on the Pipeline Quote info for the Group/Personal
namespace.

Now we're using `Namespace#actual_shared_runners_minutes_limit` which
returns the globally configured value if the current Namespace has not
been configured with CI minutes.

ee/app/models/namespace_statistics.rb

@@ -12,7 +12,7 @@ class NamespaceStatistics < ApplicationRecord
   end
 
   def extra_shared_runners_minutes
-    limit = namespace.shared_runners_minutes_limit.to_i
+    limit = namespace.actual_shared_runners_minutes_limit(include_extra: false)
     extra_limit = namespace.extra_shared_runners_minutes_limit.to_i
 
     return 0 if extra_limit.zero? || shared_runners_minutes <= limit

ee/changelogs/unreleased/rd-fix-calculation-of-extra-minutes-used-for-free-plans.yml

+---
+title: Fix calculation of used extra CI minutes
+merge_request: 14217
+author:
+type: fixed

ee/spec/models/namespace_statistics_spec.rb

@@ -46,5 +46,49 @@ describe NamespaceStatistics do
 
       it { is_expected.to eq(0) }
     end
+
+    context 'when limit is defined globally' do
+      before do
+        namespace.update_attribute(:shared_runners_minutes_limit, nil)
+
+        stub_application_setting(shared_runners_minutes: 100)
+      end
+
+      context 'when usage is above the main quota' do
+        before do
+          namespace_statistics.update_attribute(:shared_runners_seconds, 101 * 60)
+        end
+
+        context 'and extra CI minutes have been assigned' do
+          before do
+            namespace.update_attribute(:extra_shared_runners_minutes_limit, 50)
+          end
+
+          it { is_expected.to eq(1) }
+        end
+
+        context 'and extra CI minutes have not been assigned' do
+          before do
+            namespace.update_attribute(:extra_shared_runners_minutes_limit, nil)
+          end
+
+          it { is_expected.to eq(0) }
+        end
+      end
+
+      context 'when usage is below the main quota' do
+        before do
+          namespace_statistics.update_attribute(:shared_runners_seconds, 90 * 60)
+        end
+
+        context 'and extra CI minutes have been assigned' do
+          before do
+            namespace.update_attribute(:extra_shared_runners_minutes_limit, 50)
+          end
+
+          it { is_expected.to eq(0) }
+        end
+      end
+    end
   end
 end