those tests already have enough mature utxos from the pre-mined chain.
This is a partial backport of core#26886
https://github.com/bitcoin/bitcoin/pull/26886/commits/42029a7fd42e93426bdfb40d1918d739d20962af
Depends on D16025
Note that the interface_usdt_utxocache.py still needs blocks to be generated because we miss some backports (most likely culprit core#25528)