added the `allowed_error` to the `positive_env` so any tests completing
the attach are allowed have this print out. they are allowed to do so,
because the `random_init_delay` can produce close to zero and thus the
first run will be near attach. Though... Unsure if we ever really need
the eviction task to run **before** it can evict something, as in after
20min or 24h.
in the failed test case however period is 20s so interesting that we
didn't run into this sooner.
evidence of flaky:
https://github.com/neondatabase/neon/actions/runs/5175677035/jobs/9323705929?pr=4399#step:4:38536
e0bd81ce1f