Proto,Test: put back rng state to fix flakiness

Context

As the description says:

(** Regression test to ensure that we can reject a commitment where the
    proof is truncated to be close to the maximum size limit (i.e. 32Kb) and
    the rejected message size is close to the maximum size (i.e. 5Kb).

    It also test that all required parameters for the rejection fits in a
    Tezos operation even in the worst cases.
*)

It is complicated to get numbers close to this, to ensure that the test is not flaky we fixed the rng_state so the proof size and message was the same in every run. However, it was reverted in 35e8ea1c, making the test flaky.

Manually testing the MR

Checklist

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