fix(bug): Fixes panic in `new_regtest()` #1959

Job	Run time
Generate crates matrix	12s
Check crates matrix	3s
Build zebrad crate	37m 21s
Build zebra-utils crate	17m 3s
Build zebra-test crate	1m 32s
Build zebra-state crate	22m 15s
Build zebra-script crate	3m 26s
Build zebra-scan crate	27m 15s
Build zebra-rpc crate	35m 6s
Build zebra-node-services crate	3m 17s
Build zebra-network crate	7m 3s
Build zebra-grpc crate	15m 4s
Build zebra-consensus crate	17m 3s
Build zebra-chain crate	4m 51s
Build tower-fallback crate	1m 3s
Build tower-batch-control crate	1m 21s
Open or update issues for building crates individually failures	0s
	3h 13m 55s

Provide feedback