Fix shared runners duration on project list

What does this MR do and why?

After validating #370020 (closed) it was noticed a discrepancy in the shared runners numbers. Details:

This MR fixes this issue and finishes the implementation of #370020 (closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Make sure to enable: ::Gitlab::CurrentSettings.update(check_namespace_plan: true)
2. Make sure you're simulating SaaS
3. Enable the FF: Feature.enable(:usage_quotas_pipelines_vue)
4. Add some data:

   project = Project.find(108)
   root_namespace = project.root_namespace
   
   namespace_usage = Ci::Minutes::NamespaceMonthlyUsage.find_or_create_current(namespace_id: root_namespace)
   Ci::Minutes::NamespaceMonthlyUsage.update_counters(namespace_usage, shared_runners_duration: 100)
   
   project_usage = Ci::Minutes::ProjectMonthlyUsage.find_or_create_current(project_id: project)
   Ci::Minutes::ProjectMonthlyUsage.update_counters(project_usage, shared_runners_duration: 100)

5. Go to your group's usage quotas page
6. Check the project list, note the shared runners number
7. Turn off FF: Feature.disable(:usage_quotas_pipelines_vue)
8. Compare the shared runners number

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.