test: rename CBlockHeader .hash -> .hash_hex for consistency

Note that we unfortunately can't use a scripted diff here, as the
`.hash` symbol is also used for other instances (e.g. CInv).

test/functional/mining_mainnet.py

@@ -70,7 +70,7 @@ class MiningMainnetTest(BitcoinTestFramework):
         self.log.debug(block_hex)
         assert_equal(node.submitblock(block_hex), None)
         prev_hash = node.getbestblockhash()
-        assert_equal(prev_hash, block.hash)
+        assert_equal(prev_hash, block.hash_hex)
         return prev_hash