scripted-diff: validation: rename mandatory errors into block errors

Using "block" or "mempool" as the prefix in place of "mandatory" or "non-mandatory" is clearer
to a user. "non-mandatory" was renamed into "mempool" as part of #33050. This takes care of the
other half of this renaming as a scripted diff.

-BEGIN VERIFY SCRIPT-
sed -i 's/mandatory-script-verify/block-script-verify/g' $(git grep -l mandatory-script-verify)
-END VERIFY SCRIPT-

test/functional/feature_dersig.py

@@ -133,7 +133,7 @@ class BIP66Test(BitcoinTestFramework):
         block.hashMerkleRoot = block.calc_merkle_root()
         block.solve()
 
-        with self.nodes[0].assert_debug_log(expected_msgs=['Block validation error: mandatory-script-verify-flag-failed (Non-canonical DER signature)']):
+        with self.nodes[0].assert_debug_log(expected_msgs=['Block validation error: block-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()