[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_block.py

@@ -88,7 +88,6 @@ class FullBlockTest(BitcoinTestFramework):
         self.extra_args = [[
             '-acceptnonstdtxn=1',  # This is a consensus block test, we don't care about tx policy
             '-testactivationheight=bip34@2',
-            '-par=1', # Until https://github.com/bitcoin/bitcoin/issues/30960 is fixed
         ]]
 
     def run_test(self):