Use build_stubbed in CH tests

What does this MR do and why?

This MR changes the code that sets up builds that are meant to ClickHouseHelpers#insert_ci_builds_to_click_house, from using build(:ci_build) to using build_stubbed(:ci_build). One doubt I had was what would happen to build IDs. It seems that build_stubbed creates them with increments of 5, which is fine for what we need.

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