Fix create file key

What does this MR do and why?

To prevent the race condition that happens between garbage collection and mounting the volumes on the docker containers so we can have the key accessible at runtime, https://gitlab.com/gitlab-org/gitlab-qa/-/merge_requests/1176 was not sufficient to address this. This effectively copies to a File which we handle deletion right after each test run to avoid having the key lingering on the instance.

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