scripted-diff: test: Use int.to_bytes over struct packing

-BEGIN VERIFY SCRIPT-
 sed -i --regexp-extended 's!struct.pack\(.<?B., (.*)\)!\1.to_bytes(1, "little")!g'             $( git grep -l struct.pack )
 sed -i --regexp-extended 's!struct.pack\(.<I., (.*)\)!\1.to_bytes(4, "little")!g'              $( git grep -l struct.pack )
 sed -i --regexp-extended 's!struct.pack\(.<H., (.*)\)!\1.to_bytes(2, "little")!g'              $( git grep -l struct.pack )
 sed -i --regexp-extended 's!struct.pack\(.<i., (.*)\)!\1.to_bytes(4, "little", signed=True)!g' $( git grep -l struct.pack )
 sed -i --regexp-extended 's!struct.pack\(.<q., (.*)\)!\1.to_bytes(8, "little", signed=True)!g' $( git grep -l struct.pack )
 sed -i --regexp-extended 's!struct.pack\(.>H., (.*)\)!\1.to_bytes(2, "big")!g'                 $( git grep -l struct.pack )
-END VERIFY SCRIPT-

test/functional/p2p_segwit.py

@@ -1165,16 +1165,16 @@ class SegWitTest(BitcoinTestFramework):
                 if not self.wit.is_null():
                     flags |= 1
                 r = b""
-                r += struct.pack("<i", self.nVersion)
+                r += self.nVersion.to_bytes(4, "little", signed=True)
                 if flags:
                     dummy = []
                     r += ser_vector(dummy)
-                    r += struct.pack("<B", flags)
+                    r += flags.to_bytes(1, "little")
                 r += ser_vector(self.vin)
                 r += ser_vector(self.vout)
                 if flags & 1:
                     r += self.wit.serialize()
-                r += struct.pack("<I", self.nLockTime)
+                r += self.nLockTime.to_bytes(4, "little")
                 return r
 
         tx2 = BrokenCTransaction()
@@ -1976,11 +1976,11 @@ class SegWitTest(BitcoinTestFramework):
         def serialize_with_bogus_witness(tx):
             flags = 3
             r = b""
-            r += struct.pack("<i", tx.nVersion)
+            r += tx.nVersion.to_bytes(4, "little", signed=True)
             if flags:
                 dummy = []
                 r += ser_vector(dummy)
-                r += struct.pack("<B", flags)
+                r += flags.to_bytes(1, "little")
             r += ser_vector(tx.vin)
             r += ser_vector(tx.vout)
             if flags & 1:
@@ -1990,7 +1990,7 @@ class SegWitTest(BitcoinTestFramework):
                     for _ in range(len(tx.wit.vtxinwit), len(tx.vin)):
                         tx.wit.vtxinwit.append(CTxInWitness())
                 r += tx.wit.serialize()
-            r += struct.pack("<I", tx.nLockTime)
+            r += tx.nLockTime.to_bytes(4, "little")
             return r
 
         class msg_bogus_tx(msg_tx):