fix: when validating a block, clone the blocks version

Author: hstove

stackslib/src/net/api/postblock_proposal.rs

@@ -538,6 +538,7 @@ impl NakamotoBlockProposal {
         }
 
         let mut block = builder.mine_nakamoto_block(&mut tenure_tx);
+        block.header.version = self.block.header.version;
         let size = builder.get_bytes_so_far();
         let cost = builder.tenure_finish(tenure_tx)?;