chainparams: add testnet assumeutxo param at height 2_500_000

Author: Sjors

src/kernel/chainparams.cpp

@@ -267,7 +267,12 @@ class CTestNetParams : public CChainParams {
         };
 
         m_assumeutxo_data = {
-            // TODO to be specified in a future patch.
+            {
+                .height = 2'500'000,
+                .hash_serialized = AssumeutxoHash{uint256S("0x2a8fdefef3bf75fa00540ccaaaba4b5281bea94229327bdb0f7416ef1e7a645c")},
+                .nChainTx = 66484552,
+                .blockhash = uint256S("0x0000000000000093bcb68c03a9a168ae252572d348a2eaeba2cdf9231d73206f")
+            }
         };
 
         chainTxData = ChainTxData{