[backport#16465 2/3] test: Replace fragile "rng" with call to random()
[backport#16465 2/3] test: Replace fragile "rng" with call to random()

Summary:
This is a partial backport of Core [[https://github.com/bitcoin/bitcoin/pull/16465 | PR16465]] - part 2 of 3
Commit https://github.com/bitcoin/bitcoin/pull/16465/commits/fa79af298917d501cee26370fdf9d44d05133d15

Depends on D8054

Test Plan: `ninja && test/functional/test_runner.py wallet_import_rescan.py`

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D8055

Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc