ci: Fix broken master by not reading GITLAB_ENV

What does this MR do and why?

This fixes a broken master problem that started after part of the Runner fleet was updated to 16.6.0~beta.105.gd2263193: gitlab-org/quality/engineering-productivity/master-broken-incidents#4168 (comment 1646281188).

This removes the ability to read from GITLAB_ENV and always use Rails.env instead.

These variables aren't documented at all so I think this shouldn't create any problem.

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