refactor: test: use _ variable for unused loop counters

substitutes "for x in range(N):" by "for _ in range(N):"
indicates to the reader that a block is just repeated N times, and
that the loop counter is not used in the body

test/functional/wallet_labels.py

@@ -118,7 +118,7 @@ class WalletLabelsTest(BitcoinTestFramework):
         if not self.options.descriptors:
             for label in labels:
                 addresses = []
-                for x in range(10):
+                for _ in range(10):
                     addresses.append(node.getnewaddress())
                 multisig_address = node.addmultisigaddress(5, addresses, label.name)['address']
                 label.add_address(multisig_address)