feature_taproot: sample tx version border values more

Currently if the version 3 is selected for an otherwise
standard spender, the test will fail. It's unlikely but
possible, so change the test to update expectations and
sample more aggressively on border values to instigate
failures much quicker in the future if another version is
made standard.

test/functional/feature_taproot.py

@@ -642,6 +642,9 @@ SIG_ADD_ZERO = {"failure": {"sign": zero_appender(default_sign)}}
 DUST_LIMIT = 600
 MIN_FEE = 50000
 
+TX_MAX_STANDARD_VERSION = 3
+TX_STANDARD_VERSIONS = [1, 2, TX_MAX_STANDARD_VERSION]
+
 # === Actual test cases ===
 
 
@@ -1443,7 +1446,7 @@ class TaprootTest(BitcoinTestFramework):
         while left:
             # Construct CTransaction with random version, nLocktime
             tx = CTransaction()
-            tx.version = random.choice([1, 2, random.getrandbits(32)])
+            tx.version = random.choice(TX_STANDARD_VERSIONS + [0, TX_MAX_STANDARD_VERSION + 1, random.getrandbits(32)])
             min_sequence = (tx.version != 1 and tx.version != 0) * 0x80000000  # The minimum sequence number to disable relative locktime
             if random.choice([True, False]):
                 tx.nLockTime = random.randrange(LOCKTIME_THRESHOLD, self.lastblocktime - 7200)  # all absolute locktimes in the past
@@ -1535,8 +1538,7 @@ class TaprootTest(BitcoinTestFramework):
                 is_standard_tx = (
                     fail_input is None  # Must be valid to be standard
                     and (all(utxo.spender.is_standard for utxo in input_utxos))  # All inputs must be standard
-                    and tx.version >= 1  # The tx version must be standard
+                    and tx.version in TX_STANDARD_VERSIONS)  # The tx version must be standard
-                    and tx.version <= 2)
                 msg = ','.join(utxo.spender.comment + ("*" if n == fail_input else "") for n, utxo in enumerate(input_utxos))
                 if is_standard_tx:
                     node.sendrawtransaction(tx.serialize().hex(), 0)