Fix Rake/Require offense

What does this MR do and why?

This MR aims to solve the issue #391459 (closed)

This MR moves all requires into task definition of refresh_project_statistics_build_artifacts_size (lib/tasks/gitlab/refresh_project_statistics_build_artifacts_size.rake) rake task.

Screenshots

How to set up and validate locally

rake gitlab:refresh_project_statistics_build_artifacts_size\[csv_url\]

bundle exec rubocop lib/tasks/gitlab/refresh_project_statistics_build_artifacts_size.rake
Inspecting 1 file
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1 file inspected, no offenses detected

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