chainparams: Add initial minimum chain work for Testnet4

This chainwork was observed at height 38487.

Author: fjahr

src/kernel/chainparams.cpp

@@ -334,7 +334,7 @@ class CTestNet4Params : public CChainParams {
         consensus.vDeployments[Consensus::DEPLOYMENT_TAPROOT].nTimeout = Consensus::BIP9Deployment::NO_TIMEOUT;
         consensus.vDeployments[Consensus::DEPLOYMENT_TAPROOT].min_activation_height = 0; // No activation delay
 
-        consensus.nMinimumChainWork = uint256{};
+        consensus.nMinimumChainWork = uint256{"000000000000000000000000000000000000000000000056faca98a0cd9bdf5f"};
         consensus.defaultAssumeValid = uint256{};
 
         pchMessageStart[0] = 0x1c;