[validation] Make script error messages uniform for parallel/single validation

This makes the debug output mostly the same for -par=1 and parallel validation runs. Of course,
parallel validation is non-deterministic in what error it may encounter first if there are
multiple issues. Also, the way certain script-related and non-script-related checks are
performed differs between the two modes still, which may result in discrepancies.

test/functional/feature_dersig.py

@@ -51,7 +51,6 @@ class BIP66Test(BitcoinTestFramework):
         self.noban_tx_relay = True
         self.extra_args = [[
             f'-testactivationheight=dersig@{DERSIG_HEIGHT}',
-            '-par=1',  # Use only one script thread to get the exact log msg for testing
         ]]
         self.setup_clean_chain = True
         self.rpc_timeout = 240
@@ -131,7 +130,7 @@ class BIP66Test(BitcoinTestFramework):
         block.hashMerkleRoot = block.calc_merkle_root()
         block.solve()
 
-        with self.nodes[0].assert_debug_log(expected_msgs=[f'CheckInputScripts on {block.vtx[-1].hash} failed with mandatory-script-verify-flag-failed (Non-canonical DER signature)']):
+        with self.nodes[0].assert_debug_log(expected_msgs=[f'Script validation error in block: mandatory-script-verify-flag-failed (Non-canonical DER signature)']):
             peer.send_and_ping(msg_block(block))
             assert_equal(int(self.nodes[0].getbestblockhash(), 16), tip)
             peer.sync_with_ping()