Fix quarantined N+1 spec

What does this MR do and why?

This MR fixes the quarantined spec in #391442 (closed). It:

• replaces the current N+1 queries that request discrete runners with a more real-world scenario of requesting a list of runners.
• changes the spec to take cached queries into account.
• performs both GraphQL queries with the same user, since all other GraphQL N+1 specs are doing that (and it also matches the real-world usage).

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How to set up and validate locally

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Comment out the preloads. The tests should fail.