Merge bitcoin/bitcoin#29399: test: Fix utxo set hash serialisation signedness

fa0ceae970 test: Fix utxo set hash serialisation signedness (MarcoFalke)

Pull request description:

  It is unsigned in Bitcoin Core, so the tests should match it:

  5b8990a1f3/src/kernel/coinstats.cpp (L54)

  Large positive values for the block height are too difficult to hit in tests, but it still seems fine to fix this.

  The bug was introduced when the code was written in 6ccc8fc067.

  (Lowercase `i` means signed, see https://docs.python.org/3/library/struct.html#format-characters)

ACKs for top commit:
  epiccurious:
    Tested ACK fa0ceae970.
  fjahr:
    utACK fa0ceae970

Tree-SHA512: ab4405c74fb191fff8520b456d3a800cd084d616bb9ddca27d56b8e5c8969bd537490f6e204c1870dbb09a3e130b03b22a27b6644252a024059c200bbd9004e7

test/functional/feature_utxo_set_hash.py

@@ -4,8 +4,6 @@
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 """Test UTXO set hash value calculation in gettxoutsetinfo."""
 
-import struct
-
 from test_framework.messages import (
     CBlock,
     COutPoint,
@@ -58,7 +56,7 @@ class UTXOSetHashTest(BitcoinTestFramework):
                         continue
 
                     data = COutPoint(int(tx.rehash(), 16), n).serialize()
-                    data += struct.pack("<i", height * 2 + coinbase)
+                    data += (height * 2 + coinbase).to_bytes(4, "little")
                     data += tx_out.serialize()
 
                     muhash.insert(data)