Fix locking issues in DIP3 unit tests (#2285)
Fix locking issues in DIP3 unit tests (#2285)

* Don't use GetTransaction in CheckProUpRegTx

GetTransaction locks mempool.cs internally. This brings messes up the locking
order of cs_main, mempool.cs and CCheckQueue::ControlMutex.

* Lock cs_main in TestChainSetup::CreateBlock when updating CbTx

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