Merge bitcoin/bitcoin#29363: test: Fix CPartialMerkleTree.nTransactions signedness

facafa9 test: Fix CPartialMerkleTree.nTransactions signedness (MarcoFalke)

Pull request description:

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

  https://github.com/bitcoin/bitcoin/blob/aa9231fafe45513134ec8953a217cda07446fae8/src/merkleblock.h#L59

  Large positive values, or "negative" values, are rejected anyway, but it still seems fine to fix this.

  The bug was introduced when the code was written in d280617.

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

ACKs for top commit:
  theStack:
    LGTM ACK facafa9
  Empact:
    ACK facafa9

Tree-SHA512: 35ac11bb5382dffe132bfae6097efc343ef6c06b1b4b1545130ca27b228ca6894679004862fee921b095172abaddbef5972c24d9bc195ce970f35643bd4a0f09

Author: fanquake

test/functional/test_framework/messages.py

@@ -1063,7 +1063,7 @@ def __init__(self):
         self.vBits = []
 
     def deserialize(self, f):
-        self.nTransactions = int.from_bytes(f.read(4), "little", signed=True)
+        self.nTransactions = int.from_bytes(f.read(4), "little")
         self.vHash = deser_uint256_vector(f)
         vBytes = deser_string(f)
         self.vBits = []
@@ -1072,7 +1072,7 @@ def deserialize(self, f):
 
     def serialize(self):
         r = b""
-        r += self.nTransactions.to_bytes(4, "little", signed=True)
+        r += self.nTransactions.to_bytes(4, "little")
         r += ser_uint256_vector(self.vHash)
         vBytesArray = bytearray([0x00] * ((len(self.vBits) + 7)//8))
         for i in range(len(self.vBits)):